Framework: Allow choice of screen-off animation (1/2)

Adds a choice of alternative screen-off animations:

- Fade out
- Electron beam (default)
- Scale down

Change-Id: I8ec9bfc6248a1223037fd252b0c853db7994afe6

Conflicts:
	core/java/android/provider/Settings.java

Conflicts:
	packages/SystemUI/res/values/pa_strings.xml