[2/2] Camera button support

Add support for camera button

Based on commit http://review.cyanogenmod.org/#/c/52046/

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
[1/2] Camera button support in frameworks/base

Change-Id: Idb959f24fec880d360afebf194a0bc573e011438