Disable Automatic brightness checkbox if automatic brightness is not available

port from jellybean branch: http://review.cyanogenmod.org/#/c/26134/

Change-Id: Ib32b9af5f79d5c5f7383dd5542891a82a17f3989
Settings: Make it clearer how SMS Limiting works and add 500 messages option

Change-Id: Ia7458d7e7cde1cfbb6641d4b05fd9caf59d21db8