SystemUI: add Settings.System toggle for quick-quick settings pulldown

Change-Id: I3c5dcfc23f39bf8be6c402e25f61e6f57a8add2c
Signed-off-by: Roman Birg <roman@cyngn.com>

Conflicts:

	core/java/android/provider/Settings.java
	packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java