Additional changes to improve performance when loading Recents. (Bug 16987565)

- Ensuring that we consistently load activity icon, title and color for both full and shallow stacks
- Adding activity info caches when loading the stacks
- Should not be scaling pin icon when launching from pin
- Tweaking snap-back, over scroll, and shadows

Change-Id: I556b93562bb2c69e4c25ce787a7a34532ab706ca