Shuffle designation_group members into a random order

To enable a persistent random presentation of the answer options (where the members are randomly shuffled but are consistent throughout the whole survey) the question themes do this shuffling and store it in a session variable. However, this means that each question has to check whether this sorted_options variable exists and otherwise do the shuffling, also there is no way to know whether the survey is over and the session storage should be deleted. This shuffling is typically something which the plugin can do upon creating the designation groups in session storage. Then the question themes can just take the order of the designation group members as they are stored by the plugin as the persistently shuffled order, and sort them in a different way if needed and the data will be removed from the session storage as it should.