Small changes to the media player (#1572)

* Resolving some issues with media playback.

* Changing ViewVideoFragment so that it fully handles autohiding the
  media controller, allowing consistency between it and the toolbar

* Fixed an issue where the toolbar and description were not fading in

* Do not hide the toolbar/media player if the video is loading or paused

* Created "ExposedPlayPausedVideoView" to allow hooking play/pause

* Fix back button when viewing videos

* Back button did not work if video controls were visible.

* Tweak audio player

* Always show the controls when audio begins playing

* Do not auto-hide the controls if the player is playing audio

* Address PR comments

* Use overloaded constructor
* Remove m prefix

* Fix subtle media player issues

* Fix audio player incorrectly auto-hiding after hiding/showing toolbar

* Only subscribe touch listener once content is ready
  - Prevents top toolbar visibility from getting out of phase with audio player visibility if hidden during load

app/src/main/java/com/keylesspalace/tusky/ViewMediaActivity.kt

@@ -186,8 +186,14 @@ class ViewMediaActivity : BaseActivity(), ViewImageFragment.PhotoActionsListener
         for (listener in toolbarVisibilityListeners) {
             listener(isToolbarVisible)
         }
+
         val visibility = if (isToolbarVisible) View.VISIBLE else View.INVISIBLE
         val alpha = if (isToolbarVisible) 1.0f else 0.0f
+        if (isToolbarVisible) {
+            // If to be visible, need to make visible immediately and animate alpha
+            toolbar.alpha = 0.0f
+            toolbar.visibility = visibility
+        }
 
         toolbar.animate().alpha(alpha)
                 .setListener(object : AnimatorListenerAdapter() {