Camera: Change volume hard key button to zoom function

Able to capture image through volume hard key
button in camera application, change the function
to zoom function.

Change-Id: Iab9fc2492b2e2ff89cd58c21bac2f147f47b77e2

Conflicts:
	src/com/android/camera/PhotoUI.java
Camera2: implement volume key zoom in video mode

Change-Id: I140e8cfb3e39700f60e40c35b38e92c83a3c26de