code cleanup

* migrate few annotations to androidx
* mission recovery: better error handling (except StreamExtractor.getErrorMessage() method always returns an error)
* post-processing: more detailed progress

[file specific changes]

DownloadMission.java
* remove redundant/boilerplate code (again)
* make few variables volatile
* better file "length" approximation
* use "done" variable to count the amount of bytes downloaded (simplify percent calc in UI code)

Postprocessing.java
* if case of error use "ERROR_POSTPROCESSING" instead of "ERROR_UNKNOWN_EXCEPTION"
* simplify source stream init

DownloadManager.java
* move all "service message sending" code to DownloadMission
* remove not implemented method "notifyUserPendingDownloads()" also his unused strings

DownloadManagerService.java
* use START_STICKY instead of START_NOT_STICKY
* simplify addMissionEventListener()/removeMissionEventListener() methods (always are called from the main thread)

Deleter.java
* better method definition

MissionAdapter.java
* better method definition
* code cleanup
* the UI is now refreshed every 750ms
* simplify download progress calculation
* indicates if the download is actually recovering
* smooth download speed measure
* show estimated remain time

MainFragment.java:
* check if viewPager is null (issued by "Apply changes" feature of Android Studio)

app/src/main/res/values-ar/strings.xml

@@ -471,7 +471,6 @@
     <string name="error_http_not_found">غير موجود</string>
     <string name="error_postprocessing_failed">فشلت المعالجة الاولية</string>
     <string name="clear_finished_download">حذف التنزيلات المنتهية</string>
-    <string name="msg_pending_downloads">"قم بإستكمال  %s حيثما  يتم التحويل من التنزيلات"</string>
     <string name="stop">توقف</string>
     <string name="max_retry_msg">أقصى عدد للمحاولات</string>
     <string name="max_retry_desc">الحد الأقصى لعدد محاولات قبل إلغاء التحميل</string>

app/src/main/res/values-be/strings.xml

@@ -458,7 +458,6 @@
     <string name="error_http_not_found">Не знойдзена</string>
     <string name="error_postprocessing_failed">Пасляапрацоўка не ўдалася</string>
     <string name="clear_finished_download">Ачысціць завершаныя</string>
-    <string name="msg_pending_downloads">Аднавіць прыпыненыя загрузкі (%s)</string>
     <string name="stop">Спыніць</string>
     <string name="max_retry_msg">Максімум спробаў</string>
     <string name="max_retry_desc">Колькасць спробаў перад адменай загрузкі</string>

app/src/main/res/values-cmn/strings.xml

@@ -460,7 +460,6 @@
     <string name="app_update_notification_content_title">NewPipe 更新可用!</string>
     <string name="error_path_creation">无法创建目标文件夹</string>
     <string name="error_http_unsupported_range">服务器不接受多线程下载, 请使用 @string/msg_threads = 1重试</string>
-    <string name="msg_pending_downloads">继续进行%s个待下载转移</string>
     <string name="pause_downloads_on_mobile_desc">切换至移动数据时有用，尽管一些下载无法被暂停</string>
     <string name="show_comments_title">显示评论</string>
     <string name="show_comments_summary">禁用停止显示评论</string>

app/src/main/res/values-cs/strings.xml

@@ -466,7 +466,6 @@ otevření ve vyskakovacím okně</string>
     <string name="error_http_not_found">Nenalezeno</string>
     <string name="error_postprocessing_failed">Post-processing selhal</string>
     <string name="clear_finished_download">Vyčistit dokončená stahování</string>
-    <string name="msg_pending_downloads">Pokračovat ve stahování %s souborů, čekajících na stažení</string>
     <string name="stop">Zastavit</string>
     <string name="max_retry_msg">Maximální počet pokusů o opakování</string>
     <string name="max_retry_desc">Maximální počet pokusů před zrušením stahování</string>

app/src/main/res/values-da/strings.xml

@@ -447,7 +447,6 @@
     <string name="paused">sat på pause</string>
     <string name="queued">sat i kø</string>
     <string name="clear_finished_download">Ryd færdige downloads</string>
-    <string name="msg_pending_downloads">Fortsæt dine %s ventende overførsler fra Downloads</string>
     <string name="max_retry_msg">Maksimalt antal genforsøg</string>
     <string name="max_retry_desc">Maksimalt antal forsøg før downloaden opgives</string>
     <string name="pause_downloads_on_mobile">Sæt på pause ved skift til mobildata</string>

app/src/main/res/values-de/strings.xml

@@ -457,7 +457,6 @@
     <string name="error_http_not_found">Nicht gefunden</string>
     <string name="error_postprocessing_failed">Nachbearbeitung fehlgeschlagen</string>
     <string name="clear_finished_download">Um fertige Downloads bereinigen</string>
-    <string name="msg_pending_downloads">Setze deine %s ausstehenden Übertragungen von Downloads fort</string>
     <string name="stop">Anhalten</string>
     <string name="max_retry_msg">Maximale Wiederholungen</string>
     <string name="max_retry_desc">Maximalanzahl der Versuche, bevor der Download abgebrochen wird</string>

app/src/main/res/values-el/strings.xml

@@ -459,7 +459,6 @@
     <string name="error_http_not_found">Δεν βρέθηκε</string>
     <string name="error_postprocessing_failed">Μετεπεξεργασία απέτυχε</string>
     <string name="clear_finished_download">Εκκαθάριση ολοκληρωμένων λήψεων</string>
-    <string name="msg_pending_downloads">Συνέχιση των %s εκκρεμών σας λήψεων</string>
     <string name="stop">Διακοπή</string>
     <string name="max_retry_msg">Μέγιστες επαναπροσπάθειες</string>
     <string name="max_retry_desc">Μέγιστος αριθμός προσπαθειών προτού γίνει ακύρωση της λήψης</string>

app/src/main/res/values-es/strings.xml

@@ -406,6 +406,7 @@
     <string name="paused">pausado</string>
     <string name="queued">en cola</string>
     <string name="post_processing">posprocesamiento</string>
+    <string name="recovering">recuperando</string>
     <string name="enqueue">Añadir a cola</string>
     <string name="permission_denied">Acción denegada por el sistema</string>
     <string name="file_deleted">Se eliminó el archivo</string>
@@ -424,7 +425,6 @@
     <string name="grid">Mostrar como grilla</string>
     <string name="list">Mostrar como lista</string>
     <string name="clear_finished_download">Limpiar descargas finalizadas</string>
-    <string name="msg_pending_downloads">Tienes %s descargas pendientes, ve a Descargas para continuarlas</string>
     <string name="confirm_prompt">¿Lo confirma\?</string>
     <string name="stop">Detener</string>
     <string name="max_retry_msg">Intentos máximos</string>

app/src/main/res/values-et/strings.xml

@@ -460,7 +460,6 @@
     <string name="error_http_not_found">Ei leitud</string>
     <string name="error_postprocessing_failed">Järeltöötlemine nurjus</string>
     <string name="clear_finished_download">Eemalda lõpetatud allalaadimised</string>
-    <string name="msg_pending_downloads">Jätka %s pooleliolevat allalaadimist</string>
     <string name="stop">Stopp</string>
     <string name="max_retry_msg">Korduskatseid</string>
     <string name="max_retry_desc">Suurim katsete arv enne allalaadimise tühistamist</string>

app/src/main/res/values-eu/strings.xml

@@ -459,7 +459,6 @@
     <string name="error_http_not_found">Ez aurkitua</string>
     <string name="error_postprocessing_failed">Post-prozesuak huts egin du</string>
     <string name="clear_finished_download">Garbitu amaitutako deskargak</string>
-    <string name="msg_pending_downloads">Berrekin burutzeke dauden %s transferentzia deskargetatik</string>
     <string name="stop">Gelditu</string>
     <string name="max_retry_msg">Gehienezko saiakerak</string>
     <string name="max_retry_desc">Deskarga ezeztatu aurretik saiatu beharreko aldi kopurua</string>

app/src/main/res/values-fr/strings.xml

@@ -466,7 +466,6 @@
     <string name="max_retry_desc">Nombre maximum de tentatives avant d’annuler le téléchargement</string>
     <string name="saved_tabs_invalid_json">Utilisation des onglets par défaut, erreur lors de la lecture des onglets enregistrés</string>
     <string name="error_http_unsupported_range">Le serveur n’accepte pas les téléchargements multi-fils, veuillez réessayer avec @string/msg_threads = 1</string>
-    <string name="msg_pending_downloads">Continuer vos %s transferts en attente depuis Téléchargement</string>
     <string name="show_comments_title">Afficher les commentaires</string>
     <string name="show_comments_summary">Désactiver pour ne pas afficher les commentaires</string>
     <string name="autoplay_title">Lecture automatique</string>

app/src/main/res/values-he/strings.xml

@@ -464,7 +464,6 @@
     <string name="error_http_not_found">לא נמצא</string>
     <string name="error_postprocessing_failed">העיבוד המאוחר נכשל</string>
     <string name="clear_finished_download">פינוי ההורדות שהסתיימו</string>
-    <string name="msg_pending_downloads">ניתן להמשיך את %s ההורדות הממתינות שלך דרך ההורדות</string>
     <string name="stop">עצירה</string>
     <string name="max_retry_msg">מספר הניסיונות החוזרים המרבי</string>
     <string name="max_retry_desc">מספר הניסיונות החוזרים המרבי בטרם ביטול ההורדה</string>

app/src/main/res/values-hr/strings.xml

@@ -457,7 +457,6 @@
     <string name="error_http_not_found">Nije pronađeno</string>
     <string name="error_postprocessing_failed">Naknadna obrada nije uspjela</string>
     <string name="clear_finished_download">Obriši završena preuzimanja</string>
-    <string name="msg_pending_downloads">Nastavite s prijenosima na čekanju za %s s preuzimanja</string>
     <string name="stop">Stop</string>
     <string name="max_retry_msg">Maksimalnih ponovnih pokušaja</string>
     <string name="max_retry_desc">Maksimalni broj pokušaja prije poništavanja preuzimanja</string>

app/src/main/res/values-id/strings.xml

@@ -453,7 +453,6 @@
     <string name="error_http_not_found">Tidak ditemukan</string>
     <string name="error_postprocessing_failed">Pengolahan-pasca gagal</string>
     <string name="clear_finished_download">Hapus unduhan yang sudah selesai</string>
-    <string name="msg_pending_downloads">Lanjutkan %s transfer anda yang tertunda dari Unduhan</string>
     <string name="stop">Berhenti</string>
     <string name="max_retry_msg">Percobaan maksimum</string>
     <string name="max_retry_desc">Jumlah upaya maksimum sebelum membatalkan unduhan</string>

app/src/main/res/values-it/strings.xml

@@ -457,7 +457,6 @@
     <string name="error_http_not_found">Non trovato</string>
     <string name="error_postprocessing_failed">Post-processing fallito</string>
     <string name="clear_finished_download">Pulisci i download completati</string>
-    <string name="msg_pending_downloads">Continua i %s trasferimenti in corso dai Download</string>
     <string name="stop">Ferma</string>
     <string name="max_retry_msg">Tentativi massimi</string>
     <string name="max_retry_desc">Tentativi massimi prima di cancellare il download</string>

app/src/main/res/values-ja/strings.xml

@@ -456,7 +456,6 @@
     <string name="saved_tabs_invalid_json">デフォルトのタブを使用します。保存されたタブの読み込みエラーが発生しました</string>
     <string name="main_page_content_summary">メインページに表示されるタブ</string>
     <string name="updates_setting_description">新しいバージョンが利用可能なときにアプリの更新を確認する通知を表示します</string>
-    <string name="msg_pending_downloads">ダウンロードから %s の保留中の転送を続行します</string>
     <string name="pause_downloads_on_mobile">従量制課金ネットワークの割り込み</string>
     <string name="pause_downloads_on_mobile_desc">モバイルデータ通信に切り替える場合に便利ですが、一部のダウンロードは一時停止できません</string>
     <string name="show_comments_title">コメントを表示</string>

app/src/main/res/values-ko/strings.xml

@@ -454,7 +454,6 @@
     <string name="error_http_not_found">HTTP 찾을 수 없습니다</string>
     <string name="error_postprocessing_failed">후처리 작업이 실패하였습니다</string>
     <string name="clear_finished_download">완료된 다운로드 비우기</string>
-    <string name="msg_pending_downloads">대기중인 %s 다운로드를 지속하세요</string>
     <string name="stop">멈추기</string>
     <string name="max_retry_msg">최대 재시도 횟수</string>
     <string name="max_retry_desc">다운로드를 취소하기 전까지 다시 시도할 최대 횟수</string>

app/src/main/res/values-ms/strings.xml

@@ -453,7 +453,6 @@
     <string name="error_http_not_found">Tidak ditemui</string>
     <string name="error_postprocessing_failed">Pemprosesan-pasca gagal</string>
     <string name="clear_finished_download">Hapuskan senarai muat turun yang selesai</string>
-    <string name="msg_pending_downloads">Teruskan %s pemindahan anda yang menunggu dari muat turun</string>
     <string name="stop">Berhenti</string>
     <string name="max_retry_msg">Percubaan maksimum</string>
     <string name="max_retry_desc">Jumlah percubaan maksimum sebelum membatalkan muat turun</string>

app/src/main/res/values-nb-rNO/strings.xml

@@ -458,7 +458,6 @@
     <string name="error_http_not_found">Ikke funnet</string>
     <string name="error_postprocessing_failed">Etterbehandling mislyktes</string>
     <string name="clear_finished_download">Tøm fullførte nedlastinger</string>
-    <string name="msg_pending_downloads">Fortsett dine %s ventende overføringer fra Nedlastinger</string>
     <string name="stop">Stopp</string>
     <string name="max_retry_msg">Maksimalt antall forsøk</string>
     <string name="max_retry_desc">Maksimalt antall tilkoblingsforsøk før nedlastingen avblåses</string>

app/src/main/res/values-nl-rBE/strings.xml

@@ -457,7 +457,6 @@
     <string name="error_http_not_found">Niet gevonden</string>
     <string name="error_postprocessing_failed">Nabewerking mislukt</string>
     <string name="clear_finished_download">Voltooide downloads wissen</string>
-    <string name="msg_pending_downloads">Zet uw %s wachtende downloads verder via Downloads</string>
     <string name="stop">Stoppen</string>
     <string name="max_retry_msg">Maximaal aantal pogingen</string>
     <string name="max_retry_desc">Maximaal aantal pogingen vooraleer dat den download wordt geannuleerd</string>

app/src/main/res/values-nl/strings.xml

@@ -457,7 +457,6 @@
     <string name="error_http_not_found">Niet gevonden</string>
     <string name="error_postprocessing_failed">Nabewerking mislukt</string>
     <string name="clear_finished_download">Voltooide downloads wissen</string>
-    <string name="msg_pending_downloads">Zet je %s wachtende downloads voort via Downloads</string>
     <string name="stop">Stop</string>
     <string name="max_retry_msg">Maximum aantal keer proberen</string>
     <string name="max_retry_desc">Maximum aantal pogingen voordat de download wordt geannuleerd</string>

app/src/main/res/values-pa/strings.xml

@@ -453,7 +453,6 @@
     <string name="error_http_not_found">ਨਹੀਂ ਲਭਿਆ</string>
     <string name="error_postprocessing_failed">Post-processing ਫੇਲ੍ਹ</string>
     <string name="clear_finished_download">ਮੁਕੰਮਲ ਹੋਈਆਂ ਡਾਊਨਲੋਡ ਸਾਫ਼ ਕਰੋ</string>
-    <string name="msg_pending_downloads">ਡਾਉਨਲੋਡਸ ਤੋਂ ਆਪਣੀਆਂ %s ਬਕਾਇਆ ਟ੍ਰਾਂਸਫਰ ਜਾਰੀ ਰੱਖੋ</string>
     <string name="stop">ਰੁੱਕੋ</string>
     <string name="max_retry_msg">ਵੱਧ ਤੋਂ ਵੱਧ ਕੋਸ਼ਿਸ਼ਾਂ</string>
     <string name="max_retry_desc">ਡਾਉਨਲੋਡ ਰੱਦ ਕਰਨ ਤੋਂ ਪਹਿਲਾਂ ਵੱਧ ਤੋਂ ਵੱਧ ਕੋਸ਼ਿਸ਼ਾਂ</string>

app/src/main/res/values-pl/strings.xml

@@ -459,7 +459,6 @@
     <string name="error_http_not_found">Nie znaleziono</string>
     <string name="error_postprocessing_failed">Przetwarzanie końcowe nie powiodło się</string>
     <string name="clear_finished_download">Wyczyść ukończone pobieranie</string>
-    <string name="msg_pending_downloads">Kontynuuj %s oczekujące transfery z plików do pobrania</string>
     <string name="stop">Zatrzymaj</string>
     <string name="max_retry_msg">Maksymalna liczba powtórzeń</string>
     <string name="max_retry_desc">Maksymalna liczba prób przed anulowaniem pobierania</string>

app/src/main/res/values-pt-rBR/strings.xml

@@ -466,7 +466,6 @@ abrir em modo popup</string>
     <string name="error_http_not_found">Não encontrado</string>
     <string name="error_postprocessing_failed">Falha no pós processamento</string>
     <string name="clear_finished_download">Limpar downloads finalizados</string>
-    <string name="msg_pending_downloads">Continuar seus %s downloads pendentes</string>
     <string name="stop">Parar</string>
     <string name="max_retry_msg">Tentativas Máximas</string>
     <string name="max_retry_desc">Número máximo de tentativas antes de cancelar o download</string>

app/src/main/res/values-pt/strings.xml

@@ -455,7 +455,6 @@
     <string name="error_http_not_found">Não encontrado</string>
     <string name="error_postprocessing_failed">Pós-processamento falhado</string>
     <string name="clear_finished_download">Limpar transferências concluídas</string>
-    <string name="msg_pending_downloads">Continue as suas %s transferências pendentes das Transferências</string>
     <string name="stop">Parar</string>
     <string name="max_retry_msg">Tentativas máximas</string>
     <string name="max_retry_desc">Número máximo de tentativas antes de cancelar a transferência</string>

app/src/main/res/values-ru/strings.xml

@@ -464,7 +464,6 @@
     <string name="download_finished">Загрузка завершена</string>
     <string name="download_finished_more">%s загрузок завершено</string>
     <string name="generate_unique_name">Создать уникальное имя</string>
-    <string name="msg_pending_downloads">Возобновить приостановленные загрузки (%s)</string>
     <string name="max_retry_msg">Максимум попыток</string>
     <string name="max_retry_desc">Количество попыток перед отменой загрузки</string>
     <string name="pause_downloads_on_mobile_desc">Некоторые загрузки не поддерживают докачку и начнутся с начала</string>

app/src/main/res/values-sk/strings.xml

@@ -465,7 +465,6 @@
     <string name="error_http_not_found">Nenájdené</string>
     <string name="error_postprocessing_failed">Post-spracovanie zlyhalo</string>
     <string name="clear_finished_download">Vyčistiť dokončené sťahovania</string>
-    <string name="msg_pending_downloads">Pokračujte v preberaní %s zo súborov na prevzatie</string>
     <string name="stop">Stop</string>
     <string name="max_retry_msg">Maximum opakovaní</string>
     <string name="max_retry_desc">Maximálny počet pokusov pred zrušením stiahnutia</string>

app/src/main/res/values-tr/strings.xml

@@ -452,7 +452,6 @@
     <string name="error_http_not_found">Bulunamadı</string>
     <string name="error_postprocessing_failed">İşlem sonrası başarısız</string>
     <string name="clear_finished_download">Tamamlanan indirmeleri temizle</string>
-    <string name="msg_pending_downloads">Beklemedeki %s transferinize İndirmeler\'den devam edin</string>
     <string name="stop">Durdur</string>
     <string name="max_retry_msg">Azami deneme sayısı</string>
     <string name="max_retry_desc">İndirmeyi iptal etmeden önce maksimum deneme sayısı</string>

app/src/main/res/values-uk/strings.xml

@@ -471,7 +471,6 @@
     <string name="saved_tabs_invalid_json">Помилка зчитування збережених вкладок. Використовую типові вкладки.</string>
     <string name="main_page_content_summary">Вкладки, що відображаються на головній сторінці</string>
     <string name="updates_setting_description">Показувати сповіщення з пропозицією оновити застосунок за наявності нової версії</string>
-    <string name="msg_pending_downloads">Продовжити ваші %s відкладених переміщень із Завантажень</string>
     <string name="pause_downloads_on_mobile_desc">Корисно під час переходу на мобільні дані, хоча деякі завантаження не можуть бути призупинені</string>
     <string name="show_comments_title">Показувати коментарі</string>
     <string name="show_comments_summary">Вимнути відображення дописів</string>

app/src/main/res/values-vi/strings.xml

@@ -452,7 +452,6 @@
     <string name="error_http_not_found">Không tìm thấy</string>
     <string name="error_postprocessing_failed">Xử lý thất bại</string>
     <string name="clear_finished_download">Dọn các tải về đã hoàn thành</string>
-    <string name="msg_pending_downloads">Hãy tiếp tục %s tải về đang chờ</string>
     <string name="stop">Dừng</string>
     <string name="max_retry_msg">Số lượt thử lại tối đa</string>
     <string name="max_retry_desc">Số lượt thử lại trước khi hủy tải về</string>

app/src/main/res/values-zh-rTW/strings.xml

@@ -450,7 +450,6 @@
     <string name="error_http_not_found">找不到</string>
     <string name="error_postprocessing_failed">後處理失敗</string>
     <string name="clear_finished_download">清除已結束的下載</string>
-    <string name="msg_pending_downloads">繼續從您所擱置中的下載 %s 傳輸</string>
     <string name="stop">停止</string>
     <string name="max_retry_msg">最大重試次數</string>
     <string name="max_retry_desc">在取消下載前的最大嘗試數</string>

app/src/main/res/values/strings.xml

@@ -526,6 +526,7 @@
     <string name="paused">paused</string>
     <string name="queued">queued</string>
     <string name="post_processing">post-processing</string>
+    <string name="recovering">recovering</string>
     <string name="enqueue">Queue</string>
     <string name="permission_denied">Action denied by the system</string>
     <!-- download notifications -->
@@ -560,7 +561,6 @@
     <string name="error_download_resource_gone">Cannot recover this download</string>
     <string name="clear_finished_download">Clear finished downloads</string>
     <string name="confirm_prompt">Are you sure?</string>
-    <string name="msg_pending_downloads">Continue your %s pending transfers from Downloads</string>
     <string name="stop">Stop</string>
     <string name="max_retry_msg">Maximum retries</string>
     <string name="max_retry_desc">Maximum number of attempts before canceling the download</string>