This change also removes the "lockSession" method from CouchDB.
Instead, the more general update method is used which also
has the required caching annotations.

Added few pp Attributes to SessionInfo. Requests for Public Pool Sessions now return SessionInfo instead of Session.

count to NewAnswerEvent websocket broadcast. Task #14471

Updated copyright year and adjusted header format to be consistent over
all files and with other ARSnova projects.

preperation questions. Task #14343

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.

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