Add posibility to soft delete areas by owner

[bitboxer]

An owner should be able to soft delete an area. The area will then get a deleted_at flag set and the area will be hidden in the owner backend. Checkins will also not be possible anymore.

All data will be kept in the database, old checkins for those areas will be exported in the owner UI.

The admin backend should mark them as deleted so that a railslove admin can see that the area is soft deleted by the owner.