There was a bug in the session retrieval code causing an exception.

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.

**/lecturerquestion/{questionId}/answer/ for free text answers.

question object.

answers of the previous piRound were selected if no answer for the
current piRound had been saved.

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

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

Removed sessionKey from routes if it is not needed.
Changed sessionKey from PathVariable to RequestParam if still needed.
/session/{sessionKey}/question/* => /question/byaudience/*
Added redirections for legacy routes to LegacyController.

This prevents crashes caused by null pointers. Checks are moved to
the service class, and real objects are passed along.

Removed sessionKey from routes if it is not needed.
Changed sessionKey from PathVariable to RequestParam if still needed.
/session/{sessionKey}/question/* => /question/bylecturer/*

Read, unread, and total count for interposed/feedback questions
implemented.