Rework Heads up, (1/2):

Based on SlimRoms:
https://github.com/SlimRoms/frameworks_base/commit/323ed77c5e5bd6d421beae1f8118eb580be5ecf1
https://github.com/SlimRoms/frameworks_base/commit/6fb4ba4f4dfb51d2ea181be7e277e1c0c7a45761
https://github.com/SlimRoms/frameworks_base/commit/0c5054f50cbf3b8b7b9b090a1001ea23d8464252
https://github.com/SlimRoms/frameworks_base/commit/4f2025414abeb6c8df093e2efa54c63527061f00

Included:
- Remove blacklist and do not disturb feature
- Remove enable/disable heads up, (in general)
- Remove own custom time out for full screen
- Remove Heads up tile

- Add a per app based enable/disable heads up feature
  (Heads up is disabled by default for all apps,
  to enable Heads up for an app,
  long click on its notification (in the drawer),
  or at System settings -> Apps -> App details)
- Change time out values, (never, 2-, 4-, 6-, 8-, 10-, 20- or 40 seconds)
- Add an option to use the choosed time out value for full screen, too
- Add Heads up snooze function
- Add support for apps with native Heads up support

See the first SlimRoms commit for a detailed feature overview.