Settings: Toggle Stylus Pointer Icon

For devices with s-pen, this adds an option to disable
the mouse pointer when using s-pen

needs https://gerrit.slimroms.net/62

PatchSet:
- remove preference if not supported
- use onpreferencechangelistener
- minor cleanup

Change-Id: I8e752a8c8fd6a276eaf9b6bf20ad89d5ce3459ba