Halo: Add master switch to disable Halo (1/2)

Signed-off-by: Paul Beeler <sparksco@gmail.com>

Fix build
Signed-off-by: Paul Beeler <sparksco@gmail.com>

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