Settings : Add hooks for device specific features

Add support for :

Devices with bluetooth input peripherals
Devices with screen gesture support
Devices with a back touchpad

Conflicts:
	res/xml/language_settings.xml
	src/com/android/settings/cyanogenmod/ButtonSettings.java
	src/com/android/settings/cyanogenmod/SystemUiSettings.java
	src/com/android/settings/inputmethod/InputMethodAndLanguageSettings.java

Change-Id: Ia4835c69a8ba8fb76597e0ab0540f8ef1ed6e322

Conflicts:
	res/xml/system_ui_settings.xml
	src/com/android/settings/cyanogenmod/ButtonSettings.java
	src/com/android/settings/inputmethod/InputMethodAndLanguageSettings.java