Note that this is currently untested. :o

Introduced a new CouchDB view method, and a new field to divide
'skill_questions' into preparation, lecture, and flashcard
variants. The former question type 'flashcard' will be removed
soon.

Lots of redundand code deleted thanks to this change

Feedback is stored in memory on the server, and not inside
CouchDB any more.

question object.

property set.

saveQuestion, update(Question), getAnswers, saveAnswer, getMyAnswer.

This should perform much better.

LecturerQuestions and Answers to LecturerQuestions.
Renamed events concerning feedback for consistency.