Force base objects to soft delete and filter status=False out from base manager query sets.

Soft deleted objects will be removed from the index the next time that process_unindexed is run.
Replace the default delete_selected with a new soft_delete_selected method
Registrant isn't using BaseModel so it shouldn't use BaseManager.
Overwrite delete method for invoices.
Assigning owner and creator when an invoice is created
Management command to populate invoice owner
Data migration to populate the owner field for invoice
Merge branch 'refs/heads/upstream-master'