All players in one place

- main, background, popup players now connected via one service, one view, one fragment, one activity and one gesture listener
- playback position is synchronized between players. Easy to switch from one to another
- expandable player at the bottom of the screen with cool animation and additional features like long click to open channel of a video, play/pause/close buttons and swipe down to dismiss
- in-player integrated buttons for opening in browser, playing with Kodi, sharing a video
- better background playback that can be activated in settings. Allows to automatically switch to audio-only mode when going to background and then switching to video-mode when returning to the app.

app/src/main/java/org/schabi/newpipe/player/MainVideoPlayer.java

@@ -546,7 +546,7 @@ public final class MainVideoPlayer extends AppCompatActivity
                     onPlayBackgroundButtonClicked();
                     break;
                 case PlayerHelper.MinimizeMode.MINIMIZE_ON_EXIT_MODE_POPUP:
-                    onFullScreenButtonClicked();
+                    toggleFullscreen();
                     break;
                 case PlayerHelper.MinimizeMode.MINIMIZE_ON_EXIT_MODE_NONE:
                 default:
@@ -593,8 +593,8 @@ public final class MainVideoPlayer extends AppCompatActivity
         //////////////////////////////////////////////////////////////////////////*/
 
         @Override
-        public void onFullScreenButtonClicked() {
-            super.onFullScreenButtonClicked();
+        public void toggleFullscreen() {
+            super.toggleFullscreen();
 
             if (DEBUG) Log.d(TAG, "onFullScreenButtonClicked() called");
             if (simpleExoPlayer == null) return;
@@ -678,7 +678,7 @@ public final class MainVideoPlayer extends AppCompatActivity
                 onScreenRotationClicked();
 
             } else if (v.getId() == switchPopupButton.getId()) {
-                onFullScreenButtonClicked();
+                toggleFullscreen();
 
             } else if (v.getId() == switchBackgroundButton.getId()) {
                 onPlayBackgroundButtonClicked();
@@ -746,7 +746,7 @@ public final class MainVideoPlayer extends AppCompatActivity
         @Override
         public void onPlaybackSpeedClicked() {
             PlaybackParameterDialog
-                    .newInstance(getPlaybackSpeed(), getPlaybackPitch(), getPlaybackSkipSilence())
+                    .newInstance(getPlaybackSpeed(), getPlaybackPitch(), getPlaybackSkipSilence(), MainVideoPlayer.this)
                     .show(getSupportFragmentManager(), TAG);
         }
 
@@ -909,6 +909,9 @@ public final class MainVideoPlayer extends AppCompatActivity
             );
         }
 
+        @Override
+        public void hideSystemUIIfNeeded() { }
+
         private void updatePlaybackButtons() {
             if (repeatButton == null || shuffleButton == null ||
                     simpleExoPlayer == null || playQueue == null) return;