Process elements in Service

[leonlatsch]

Maybe, we should move the logic from the process dialogs to a foreground service. This way, it wont be aborted, when pressing the home button.

The Nofication should look like the one from Nextcloud when uploading files:

TODO's:

• [ ] Create Mockups
• [ ] Technical Concept
• [ ] Design Small icon for notification
• [ ] Implmentation