Resolve issues with deleting an edition
Summary
Deleting an edition does not do a cascading delete on roles, leading to NPE later in e.g. history views in Queue (see queue#524 (closed) )
Steps to Reproduce
- put people in edition
- delete edition
- go to history of a student in that deleted edition
- see error
Possible Fix
- prevent deletion if edition has roles; suggest archiving instead
- or: delete roles if edition gets deleted (get confirmation of admin?)