change getQuestionsBySortOrder to fetch Questions in one single db request instead of requesting every document alone

Removed test cases because they weren't of much use after
the refactoring.

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.

preperation questions. Task #14343