Trebuchet: add lockscreen wallpaper picker

Change-Id: Ic4f2589924a3c61b676db907f08108286dc45c29
Signed-off-by: Roman Birg <roman@cyngn.com>
Trebuchet : Destroy cropview to avoid leaks in picker

If the cropview's TiledImageRenderer is rendering threads, the activity
context gets leaked. Avoid that by invoking its destroy in onDestroy() of activity.

Change-Id: I8503e88d1cab7fc8dab61ba7da148579902f0477