Task #4027: getQuestionById fixes if a list of answers exist which could
not morphed by self

The new NoContentException should indicate, that there is no error, but
the server could not provide a response object. This will result in
HTTP Code 204 - NO CONTENT => see RFC2616

Fixed two NullPointerExceptions wich might occure in QuestionService or
by using CouchDBDao from QuestionService.

check if session has this question and throw unauthorized exception if
not

add type of user account
adjust test for new user account type
UserServiceTest which test persistence of the maps

This provides smaller and cleaner Interfaces for each context.