Themes: add ability to theme quick settings battery tiles

This is to make the battery tiles more uniform to the rest
of quick settings and also allow the background to be themed

http://i.imgur.com/AA5bkMK.png

Change-Id: Iec03572a0fa3619d2652f30b6c260a278ed0c86b

Conflicts:
	packages/SystemUI/res/layout/quick_settings_tile_battery.xml
	packages/SystemUI/res/layout/quick_settings_tile_dock_battery.xml
	packages/SystemUI/src/com/android/systemui/quicksettings/BatteryTile.java