More cleanups and finish

* Ship some more default rules in plasmanotifyrc
* Improved do not disturb menu (add "for 4 hours" and "until disabled")
* Expand unread notifications by default, overall improved expansion/collapse handling
* Show unread count in panel and reset when plasmoid is closed again
* Move notification sanitizer and its test from dataengine to lib
* Load pixmaps into model also for files and limit their physical size
* Enforce maximum limit for notifications (1000...)