#15391 add null-query to not get nullpointerexception and rework getQuestionBySortOrder and some minor bugs

#15362 alphabetical sortOrder is now automatically created when there is no sortOrder. bugfix included

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.