Allow users to delete a repository

This needs to be implemented with care as things need to be deleted from the file system in various places.

Related to #75 (closed).

mentioned in issue #75 (closed)

changed title from Add button to delete repo in repo info view to Allow users to delete a repository

changed the description

added feature label

changed milestone to %1.0

added dev label

added Doing and removed ~2112488 labels

assigned to @NicoAlt

Please don't forget to add tests when implementing this.

removed Doing label