Gallery2: add some video features

including: previous/next video play mode, screen mode,
fast forward/rewind button, step settings.

Change-Id: I3f4890c4dd95956e0eca889a5fd8b8d83b8d542e
MoviePlayer: Flush UI display after suspend/resume

- Post mPlayingCheck again in onResume() for HTTP streaming
- To disable the "Loading" pattern after resume

Change-Id: Ic0e5bd0bb0710d76f41a40249022526b4d4e71db