Add auditable superuser mode (#824)

* Remove is_superuser everywhere

* Session handling

* List of sessions, relative timeout

* Absolute timeout

* Optionally pseudo-force audit comments

* Fix failing tests

* Add tests

* Add docs

* Rebsae migration

* Typos

* Fix tests

src/tests/control/test_views.py

@@ -65,6 +65,7 @@ def logged_in_client(client, event):
     )
     t.members.add(user)
     client.force_login(user)
+    user.staffsession_set.create(date_start=now(), session_key=client.session.session_key)
     return client