Update Message for ongoing tasks

**Is your feature request related to a problem? Please describe.**
My backup-program creates multiple notifications. Currently each time a new state is reached, a new notification is created. This creates many single entries that can get quiet cluttered.

**Describe the solution you'd like**
If an app creates a message, it should return the messageid. This messageid can then be used to update said message. The client simply acts as if a new message arrived, and removes the old one.