SystemUI: Expose heads up.

Signed-off-by: Roman Birg <roman@cyngn.com>
Signed-off-by: Adnan Begovic <adnan@cyngn.com>
Change-Id: I276cb1c80d392b7dbac28e5f553207415b558481

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java
	packages/SystemUI/src/com/android/systemui/statusbar/tv/TvStatusBar.java