Reset or generate new contest

Allow resetting the contest via Django back-end as in swiping the DB (QSOs, Shadow Calls, References, Users except admins)
- Current state: Delete DB entries via admin interface:
  - QSOs
  - Shadow Calls
  - References
  - Users
- Rename Contest via "Contests"
Adding a new contest archives the old one
Change dates and e.g. contest rules as part of the contest options in Django

Edited Jan 20, 2020 by Sebastian Lange (DL7BST)