Option to set notification icon opacity 1/2 - Picked from CarbonRom

Change-Id: If2f251b2187524b153a695977f3ee9ce5bf487db

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/StatusBarIconView.java

Conflicts:
	core/java/android/provider/Settings.java
	packages/SystemUI/src/com/android/systemui/statusbar/StatusBarIconView.java