Settings: Heads Up background color && transparency [1/2]

PS12: squash dependency - heads up settings now under interface menu

PS: add ability to set custom heads up text color

Change-Id: I606bf35d5db9a253448971bdedf6fdb3acad6452

Conflicts:
	res/values/slim_strings.xml
	res/xml/heads_up_settings.xml
	src/com/android/settings/slim/HeadsUp.java