Add API demo for game style system UI interaction.

Shows the ideal way for a game to interact with system UI, hiding
the status bar and nav bar while being played, making them visible
when paused or otherwise interacting with controls of the game,
and determing layout of game controls to not be covered by the
status bar or nav bar.

Change-Id: Ia192c31321113d81f96c06c7a69a06ef72c4682a
4 files changed