Implement all the things

- Notification action buttons
- Custom icon pixmaps in notifications
- Popup handling
- Notification urgency (low isn't shown as popup TBD, critical always no matter what)
- History stuff (only expired notifications end up there, none that were closed or revoked)
- Text selection and copy for body text
- Basic tray icon support
and many other things

Application jobs are shown as part of regular notifications:
- They show up as little popup that can be hidden in the history
- When finished progress popup turns into a notification

There's still some glitches and missing features, notably
- Screenshot thumbnails
- "Open" functionality for finished jobs
- History layout
- code cleanup
- and basically every configuration option