Add play icon to the gesture settings videos.

1. Add a play button icon to show on top of the gesture videos when the
video is not playing.
2. Dynamically split the gesture video and description text in half
instead of using the hard coded value.
3. Hide the video view if animation is not available.
4. Delay removing the animation preview till the video starts drawing on
the surface texture.

Bug: 28565958
Change-Id: I8b954828d16286014404172d29efa4d2e00432b3