Implementing Recents focus states. (Bug 16950262)

- Fixed issue with focus going to send front most task when coming from Home
- Adding shortcut to dismiss a task
- Refactoring code to get secondary overlay and affiliation color
- Throttling alt-tab key presses
- Fixing issue with slivers of the task thumbnail being visible for affiliated tasks

Change-Id: Iaafe408318646a423fd58b51bbe93dbe0f2eed99