#47: Implement /messages/:id (get) and mocha tests
#50: Implement /messages/inbox/:membername (get) and mocha tests
#51: Implement /messages/to/:membername (get)
#52: Implement /messages/from/:membername (get)
#39: Implement /participants/:membername/:challenge_id/deliverables (get)
#36: Implement /participants/:membername/:challenge_id (get)