Use vector drawables instead of PNGs for material icons

For all manually-created images PNG have been kept.
- rename all icon attrs to have a `ic_` prefix
- always use `_24dp` icons, because there is no real difference, since they are vector drawables
- always use the original name found on material.io for icon drawables, as to not create confusion and possibly duplicates. Icon names can still be different from real drawable names, though I have made some of them compliant to this or maybe more meaningul.
- remove duplicate `getIconByAttr()` in ThemeHelper (use `resolveResourceIdFromAttr()`
- use standard icons for `expand_more` and `expand_less` instead of triangles
- use `play_button_outline` instead of custom PNG as play button in VideoDetailFragment (questionable, as there is no shadow anymore)

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

@@ -11,13 +11,13 @@
 
     <item android:id="@+id/start_downloads"
         android:visible="false"
-        android:icon="?attr/play"
+        android:icon="?attr/ic_play_arrow"
         android:title="@string/start_downloads"
         app:showAsAction="ifRoom" />
 
     <item android:id="@+id/pause_downloads"
         android:visible="false"
-        android:icon="?attr/pause"
+        android:icon="?attr/ic_pause"
         android:title="@string/pause_downloads"
         app:showAsAction="ifRoom" />
 

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

@@ -5,5 +5,5 @@
     <item android:id="@+id/menu_item_share_error"
         android:title="@string/share"
         app:showAsAction="ifRoom"
-        android:icon="?attr/share"/>
+        android:icon="?attr/ic_share"/>
 </menu>

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

@@ -4,7 +4,7 @@
 
     <item
         android:id="@+id/action_search"
-        android:icon="?attr/search"
+        android:icon="?attr/ic_search"
         android:orderInCategory="1"
         android:title="@string/search"
         app:showAsAction="always"/>

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

@@ -6,7 +6,7 @@
 
     <item
         android:id="@+id/menu_item_rss"
-        android:icon="?attr/rss"
+        android:icon="?attr/ic_rss"
         android:title="@string/rss_button_title"
         android:visible="false"
         app:showAsAction="ifRoom"
@@ -14,7 +14,7 @@
 
     <item
         android:id="@+id/menu_item_share"
-        android:icon="?attr/share"
+        android:icon="?attr/ic_share"
         android:title="@string/share"
         app:showAsAction="ifRoom"/>
 

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

@@ -12,7 +12,7 @@
 
     <item
         android:id="@+id/action_mute"
-        android:icon="?attr/volume_off"
+        android:icon="?attr/ic_volume_off"
         android:title="@string/mute"
         android:visible="true"
         app:showAsAction="ifRoom"/>

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

@@ -5,7 +5,7 @@
 
     <item
         android:id="@+id/menu_item_share"
-        android:icon="?attr/share"
+        android:icon="?attr/ic_share"
         android:title="@string/share"
         app:showAsAction="ifRoom"/>
 

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

@@ -4,7 +4,7 @@
 
     <item
         android:id="@+id/filter"
-        android:icon="?attr/filter"
+        android:icon="?attr/ic_filter_list"
         android:title="@string/filter"
         app:showAsAction="always">
         <menu>

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

@@ -5,17 +5,17 @@
     xmlns:app="http://schemas.android.com/apk/res-auto">
     <item
         android:id="@+id/toggleOrientation"
-        android:icon="@drawable/ic_screen_rotation_white"
+        android:icon="@drawable/ic_screen_rotation_white_24dp"
         android:title="@string/toggle_orientation"
         app:showAsAction="ifRoom|withText" />
     <item
         android:id="@+id/switchPopup"
-        android:icon="@drawable/ic_fullscreen_exit_white"
+        android:icon="@drawable/ic_fullscreen_exit_white_24dp"
         android:title="@string/switch_to_popup"
         app:showAsAction="ifRoom|withText" />
     <item
         android:id="@+id/switchBackground"
-        android:icon="?audio"
+        android:icon="?attr/ic_headset"
         android:title="@string/switch_to_background"
         app:showAsAction="ifRoom|withText" />
 </menu>

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

@@ -4,13 +4,13 @@
 
     <item
         android:id="@+id/action_play_with_kodi"
-        android:icon="?attr/cast"
+        android:icon="?attr/ic_cast"
         android:title="@string/play_with_kodi_title"
         app:showAsAction="ifRoom"/>
 
     <item
         android:id="@+id/menu_item_share"
-        android:icon="?attr/share"
+        android:icon="?attr/ic_share"
         android:title="@string/share"
         app:showAsAction="ifRoom"/>
 

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

@@ -1,9 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<menu xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:app="http://schemas.android.com/apk/res-auto">
-
-    <item android:id="@+id/menu_item_screen_rotation"
-        android:title="@string/screen_rotation"
-        app:showAsAction="always"
-        android:icon="@drawable/ic_screen_rotation_white"/>
-</menu>