Better usage of cache for groups and clubs related operations (#634)

* Better usage of cache for group retrieval

* Cache clearing on object deletion or update

* replace signals by save and delete override

* add is_anonymous check in is_owned_by

Add in many is_owned_by(self, user) methods that user is not anonymous. Since many of those functions do db queries, this should reduce a little bit the load of the db.

* Stricter usage of User.is_in_group

Constrain the parameters that can be passed to the function to make sure only a str or an int can be used. Also force to explicitly specify if the group id or the group name is used.

* write test and correct bugs

* remove forgotten populate commands

* Correct test

club/views.py

@@ -306,9 +306,7 @@ class ClubMembersView(ClubTabsMixin, CanViewMixin, DetailFormView):
         return resp
 
     def dispatch(self, request, *args, **kwargs):
-        self.members = (
-            self.get_object().members.filter(end_date=None).order_by("-role").all()
-        )
+        self.members = self.get_object().members.ongoing().order_by("-role")
         return super(ClubMembersView, self).dispatch(request, *args, **kwargs)
 
     def get_success_url(self, **kwargs):