TMSS-322: reimplemented this feature. As stated in the ticket: such a...
TMSS-322: reimplemented this feature. As stated in the ticket: such a convenience log_url is not part of the Subtask model, but can be a view on the model. So, implemeted it in the viewset. Now, fetching subtasks from the TMSS db is superfast again.
See also previous merge request for previous implementation: !245 (merged)
Closes TMSS-322 (again)