Rework Heads up, (2/2):

Based on SlimRoms:
https://github.com/SlimRoms/packages_apps_Settings/commit/b5eacf0b6a89b8531cbbb8693ec2e096d719eeba

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 support for apps with native Heads up support
- Use a better handling for the time out summary, (like the snooze summery handling)