Collective soft deletion
Instead of instantly deleting a collective, we want a soft deletion: after soft delete, the collective is still there, but not accessible anymore. It's listed in the collectives trash (below collectives list) with three options:
- restore collective
- permanently delete collective
- permanently delete collective and circle
The button for soft delete could be something like "move to trash".
The garbage collector should remove collectives (but not their circle!) from the trash according to the instance-wide retention time settings.