Merge branch 'Feature#14773' of scm.thm.de:arsnova/swtp2015-text-checker-arsnova-backend into Feature#14773

#14886 edited the lecture/preparation view to use new sort_question-views, saveOrder is not checking whether there is already a list

The delayed pi-round change can now be triggered via a simple api call.
After the api call a timed task will be started, which executes the
necessary steps for a round change. 

#14886 edited the lecture/preparation view to use new sort_question-views, saveOrder is not checking whether there is already a list

Previously, a single wrong answer was sufficient for a
question to get a 0% score. With this change, they
are counted as much as a correct answer. The only
difference now is that they reduce the overall
score of a question. See test cases for a
few examples.

The numbers for 'sessions' and 'questions' are now
derived from their underlying elements:
- open/closed for sessions
- lecture/preparation for questions

Removed test cases because they weren't of much use after
the refactoring.