title: Add button for full screen video with exo player
body: <p>I'm using exoPlayer to stream video to my app and so far works fine. What I would like to do now is to add some extra functionality such as a button on the bottom right edge to act as a "full screen button".</p>
  
  <p>But there are two problems. The first is that <code>ExoPlayer</code> doesn't seems to provide any Control class so you can simple add a button and override its functionality. 
  What I guess is that I have to display that button on top of the video so I might have to wrap both in a <code>FrameLayout</code> and add gravity = bottom for the button or is there another way ? </p>
  
  <p>The second problem is : if user clicks the full screen button what should I do next? Add another <code>Fragment</code> with the video view in full screen ? But how can I start the video from the point it was when user click the button and not start it from the beginning ?  I cant find in exoPlayer anything relative to start from a specific time.</p>