Add back hardware key settings.

Change-Id: I925fd9d9c02b86d8e93c8b9e25870433f7c20bde

Conflicts:
	proguard.flags
	res/values/cm_arrays.xml
	res/values/cm_strings.xml
	res/values/config.xml
	res/xml/button_settings.xml
	src/com/android/settings/cyanogenmod/ButtonSettings.java