Refactoring for dasf-messaging-python master branch

Hey @daniel-eggert! way to much time passed since I worked on this last time... But this week I definitely need to get something done such that we can migrate the backend module away from the legacy framework. My plan is to start with this progress-api. But since so much time passed, it would be great if we could arrange a short meeting on Wednesday or Thursday. what do you think? What about @nils-brinckmann?