[ExoPlayer] Value of paused prop should be respected when resuming the app (#486)

Before, when you resumed the app the player would **always** start playing again.

After this changed the `paused` prop of the `Video` component (which is the `isPaused` variable internally)
is consulted on resume for whether or not the playback should resume as well.

android-exoplayer/src/main/java/com/brentvatne/exoplayer/ReactExoplayerView.java

@@ -171,7 +171,7 @@ class ReactExoplayerView extends FrameLayout implements
 
     @Override
     public void onHostResume() {
-        startPlayback();
+        setPlayWhenReady(!isPaused);
     }
 
     @Override