Active display: Ability to turn off the screen, when a not clearable notification is present

Removing the last clearable notification in AD turns of the screen. But if there is a not clearable notification, there is no ability to turn it off directly.
This patch adds a power target on place of the 'clear notification' target of AD.

Change-Id: I807cca4c293ed732b441cfdcca50957b427809fa

Conflicts:

	packages/SystemUI/res/drawable-hdpi/ic_qs_power.png
	packages/SystemUI/res/drawable-mdpi/ic_qs_power.png
	packages/SystemUI/res/drawable-xhdpi/ic_qs_power.png