Settings: Add HeadsUp setting.

Change-Id: Ib7a59145843bedb16aacc87bf6d3c6da143e8d3e

Conflicts:
	res/values/cm_strings.xml
	res/xml/notification_drawer.xml

Conflicts:
	res/values/bs_strings.xml
	res/xml/misc_tweaks.xml
	res/xml/notification_drawer_qs_settings.xml