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/view/ExposedPlayPauseVideoView.kt

@@ -0,0 +1,33 @@
+package com.keylesspalace.tusky.view
+
+import android.content.Context
+import android.util.AttributeSet
+import android.widget.VideoView
+
+class ExposedPlayPauseVideoView @JvmOverloads constructor(
+        context: Context,
+        attrs: AttributeSet? = null,
+        defStyleAttr: Int = 0)
+    : VideoView(context, attrs, defStyleAttr) {
+
+    private var listener: PlayPauseListener? = null
+
+    fun setPlayPauseListener(listener: PlayPauseListener) {
+        this.listener = listener
+    }
+
+    override fun start() {
+        super.start()
+        listener?.onPlay()
+    }
+
+    override fun pause() {
+        super.pause()
+        listener?.onPause()
+    }
+
+    interface PlayPauseListener {
+        fun onPlay()
+        fun onPause()
+    }
+}