Include a way to get set members and answers for concept

Right now all of the sets associated with concept except set members and answers are returned in both the default and full representations. The set boolean is also included.

I don't believe either set members or answers should be sub-resources because their type is concept. Rather, I believe they should be presented as reference lists (that is, a list of set members or answers in the reference representation). I am willing to see both be present only in the full representation, so long as there is a hasAnswers boolean in the default representation. This would have to be a calculated field in Concept.hbm.xml with a getter in Concept.java.

These changes are needed for the JSS project, so if we don't want to make and backport any changes to Concept, I suggest that we add both reference lists to both the default and full representations.