[2/2] ElectronBeam: Add an alternative screen-off animation

Adds a selector to choose the screen-off animation.

Change-Id: I5109ca899a75dae2e991ca57811acd57af10a48b

Conflicts:

	res/values/custom_strings.xml
	res/xml/display_settings.xml
	src/com/android/settings/DisplaySettings.java