Closes #128 (closed)
This MR will change a basic functionality in the project. Merging this will delete the in-memory-data-service. This means that all the requests to the old, local db will crash unless it is already changed to the new api routes of the ARSnova backend
If you want to work at any api issue, use THIS BRANCH as base branch! This branch will be merged along with all other api branches as soon as they are all ready!