Implement more missing stuff and be more spec-compliant

- Support replacing notifications properly
  - Now that we have nice models we can finally do the replacing in the way the spec
  asks for "atomically (ie with no flicker or other visual cues)"
- Catch some more cases in notification details text (trash:/ stuff)
- Prefer notifyrc name over desktop entry name in case a service within another app sends
  an event (e.g. Discover notifier in Plasma, KNotification automatically sends desktop-entry
  of the parent app)
- Implement x-kde-urls thumbnailer with drag and drop and fancy blur
  Originally intended to be able to show multiple files but in practise only used for
  single pictures, so the code is significantly simplified for that usecase
- Add "Open" feature for finished job notification, offers a context menu as well with
  all the KFileItemActions (component from the Thumbnailer)
- Copy description labels to clipboard
  Once menu opens the update is paused so the text you copy is what you see
- Fixup sanitizer so we can properly collapse notifications without body text

... and more