#37: Implement /participants/:membername/:challenge_id (post)
#38: Implement /participants/:membername/:challenge_id (put)
#40 Implement /participants/:membername/:challenge_id/deliverables (post)
Moved endpoint to correct file
Switched implementation to pg (POST /participants/:membername/:challenge_id/deliverables)
Made data parameter accept json for endpoint PUT /participants/:membername/:challenge_id/deliverables