Settings: Add Home/Back buttons available for rebinding (2/2)

This also removes the Kill App Longpress Back toggle in Development Settings since it is now a bindable action.
Preview of settings: http://goo.gl/uvrjF

Patchsets:
- rebase

Change-Id: Ief2f827e29ece715dc7a58b0997f1fbee89a4208

Conflicts:
	res/values/arrays.xml
	res/values/strings.xml