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

Change-Id: Ia4835c69a8ba8fb76597e0ab0540f8ef1ed6e322
not needed

Change-Id: I284e37ff418a2434912a6b181e4e0604454903be
Bluetooth: Don't set a null alias before unpairing

* This causes the unpair action to throw a null pointer exception and
  bring down the Settings app. Don't do this.

Change-Id: I0c60437f5ea934385a037a464743e24c9d341aca