Camera button support

Add support for camera button

Based on commit http://review.cyanogenmod.org/#/c/51487/

This patch adds:
- Use camera button as wake key
- Use focus button as peek and wake key
- Use camera button to launch (secure) camera

Depends on:
[2/2] Camera button support in packages/apps/Settings

Change-Id: Ia515c04cca098bf0d20b077ebffc079ee4008f21