lockscreen: new Ring style (1/3)

Introduces a new Ring style - 2 rings on left/right to unlock/silence.
1 ring in the middle to launch up to 4 custom apps.
Rings can be dragged anywhere on lockscreen - not just in one direction.
Unlock/silence rings are triggered by dragging the ring far enough away from its neutral position.
Custom apps are triggered by releasing the middle ring while over the app icon.

Demo video: http://www.youtube.com/watch?v=VnQzT9QyJFQ

EDIT: Now hides album art if custom apps ring is enabled.
EDIT 2: Better layout of custom app rings for 1-3 custom apps,
        New bubbly drawables by Prash!
EDIT 3: Screen stays on while dragging rings

Change-Id: I6cf3b61e7478731e876b14f9e5bd32eaaf3edf12