Settings: Heads up meets SlimKat....SlimKat meets Google IO [4/4]

For detailed explanation see here: https://gerrit.slimroms.net/#/c/9937/

5. Add in app info screen a checkbox to enable heads up for the app.
   As another possibility aside the longpress on the notification on
   notification drawer.

Change-Id: I999df799cecb487c502e4a77626445813eeb197f