New MP4 muxer + Queue changes + Storage fixes

Main changes:
* correctly check the available space (CircularFile.java)
* misc cleanup (CircularFile.java)
* use the "Error Reporter" for non-http errors
* rewrite network state checking and add better support for API 21 (Lollipop) or higher
* implement "metered networks"
* add buttons in "Downloads" activity to start/pause all pending downloads, ignoring the queue flag or if the network is "metered"
* add workaround for VPN connections and/or network switching. Example: switching WiFi to 3G
* rewrite DataReader ¡Webm muxer is now 57% more faster!
* rewrite CircularFile, use file buffers instead of memory buffers. Less troubles in low-end devices
* fix missing offset for KaxCluster (WebMWriter.java), manifested as no thumbnails on file explorers

Download queue:
* remember queue status, unless the user pause the download (un-queue)
* semi-automatic downloads, between networks. Effective if the user create a new download or the downloads activity is starts
* allow enqueue failed downloads
* new option, queue limit, enabled by default. Used to allow one or multiple downloads at same time

Miscellaneous:
* fix crash while selecting details/error menu (mistake on MissionFragment.java)
* misc serialize changes (DownloadMission.java)
* minor UI tweaks
* allow overwrite paused downloads
* fix wrong icons for grid/list button in downloads
* add share option
* implement #2006
* correct misspelled word in strings.xml (es) (cmn)
* fix MissionAdapter crash during device shutdown

New Mp4Muxer + required changes:
* new mp4 muxer (from dash only) with this, muxing on Android 7 is possible now!!!
* re-work in SharpStream
* drop mp4 dash muxer
* misc changes: add warning in SecondaryStreamHelper.java,
* strip m4a DASH files to normal m4a format (youtube only)

Fix storage issues:
* warn to the user if is choosing a "read only" download directory (for external SD Cards), useless is rooted :)
* "write proof" allow post-processing resuming only if the device ran out of space
* implement "insufficient storage" error for downloads

app/src/main/res/menu/download_menu.xml

@@ -7,6 +7,18 @@
         android:title="@string/grid"
         app:showAsAction="ifRoom" />
 
+    <item android:id="@+id/start_downloads"
+        android:visible="false"
+        android:icon="?attr/play"
+        android:title="@string/start_downloads"
+        app:showAsAction="ifRoom" />
+
+    <item android:id="@+id/pause_downloads"
+        android:visible="false"
+        android:icon="?attr/pause"
+        android:title="@string/pause_downloads"
+        app:showAsAction="ifRoom" />
+
     <item android:id="@+id/clear_list"
         android:visible="false"
         android:icon="?attr/ic_delete"

app/src/main/res/menu/mission.xml

@@ -1,4 +1,13 @@
 <menu xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <item
+        android:id="@+id/retry"
+        android:title="@string/retry" />
+
+    <item
+        android:id="@+id/cancel"
+        android:title="@string/cancel" />
+
     <item
         android:id="@+id/start"
         android:title="@string/start" />
@@ -13,8 +22,8 @@
         android:checkable="true"/>
 
     <item
-        android:id="@+id/open"
-        android:title="@string/view" />
+        android:id="@+id/menu_item_share"
+        android:title="@string/share" />
 
     <item
         android:id="@+id/delete"