ability to remove halo and add it back

Change-Id: I8b523c000dae593f8f5fe623ca1fcfb706a19180

Conflicts:
	core/java/android/provider/Settings.java
	packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java
	packages/SystemUI/src/com/android/systemui/statusbar/halo/Halo.java