Archive old Sprints
Make it possible to archive old sprints to boost system performance for long-running projects.
Acceptance tests
- Add "Archive" action to past Sprints.
- Archived Sprints must be vieweable in HTML format.
- All entities from archived Sprints must be removed removed.
- The software shall handle references to removed entities correctly (links in text, affiliation with other entities, ...). Is it possible to link existing textual references to their archive locations?