Update designation group data format

The new version of the QANS authentication plugin stores the designation group data in a slightly different format to the session storage. Changes are:

• an additional layer containing "size" and "members" items under the relation type. The "members" items holds the original list of dicts with "short_id" and "display_name".
• Also, the relation type is given in plural ("classmates" instead of "classmate"). This needs to be accounted for in the question themes as well.