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

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.

This will result in events being fired at the right time.
Most importantly, this ensures event-specific caching
annotations to work correctly.

This also fixes a test error.

Caching was too aggressive. However, the database
has been asked for session info even if there
were no actual sessions! A simple check now saves
four immediate CouchDB requests.