Order MemberGroup by name by default.

This wasn't ideal for the old i18n-capable version of concrexit,
but we dropped that so the comment is outdated.

This does likely mean some redundant sorting is done, but that's not an
issue.

website/activemembers/models.py

@@ -168,7 +168,7 @@ def get_absolute_url(self):
     class Meta:
         verbose_name = _("member group")
         verbose_name_plural = _("member groups")
-        # ordering is done in the manager, to sort on a translated field
+        ordering = ["name"]
 
 
 class Committee(MemberGroup):