galaxys2: advanced settings: add content adaptive backlight control

Change-Id: I325d9663d7d1b82a7ebfb112e983a485689b063b

Conflicts:
	DeviceSettings/res/values/strings.xml
	DeviceSettings/res/xml/screen_preferences.xml
	DeviceSettings/src/com/cyanogenmod/settings/device/DeviceSettings.java
	DeviceSettings/src/com/cyanogenmod/settings/device/ScreenFragmentActivity.java
	DeviceSettings/src/com/cyanogenmod/settings/device/Startup.java