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

accounting/templates/accounting/bank_account_details.jinja

@@ -12,7 +12,7 @@
         </p>
         <hr>
         <h2>{% trans %}Bank account: {% endtrans %}{{ object.name }}</h2>
-        {% if user.is_in_group(settings.SITH_GROUP_ACCOUNTING_ADMIN_ID) and not object.club_accounts.exists() %}
+        {% if user.is_in_group(pk=settings.SITH_GROUP_ACCOUNTING_ADMIN_ID) and not object.club_accounts.exists() %}
         <a href="{{ url('accounting:bank_delete', b_account_id=object.id) }}">{% trans %}Delete{% endtrans %}</a>
         {% endif %}
         <h4>{% trans %}Infos{% endtrans %}</h4>