Camera button support: useful features & bugfixes (1/2)

Screw the remapping, let's make something more useful!
Replaced the code to actually launch Camera app, not just fire the shutter.
I won't remove it: it's cool to have an option to double-click Home for Camera.
Added:
  * Camera wake (with button half-press) and unlock options
  * "Peek": releasing the half-pressed Camera button will
    turn the screen back off
  * Camera playback control

Change-Id: Id49e09e20d81cd80d9800ab8ab0f200d44485a09