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

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

This patch adds the 4 possible user configurable settings.

1. Enable always expanded heads up notifications.
2. Set heads up snooze time
3. Set timout timer
4. Show updates of pending notifications

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