Nuance - federate out the design of NuanceSource via NuanceSourceDefinition

Summary: ...and get the basic edit flow "working" for a new NuanceSourceDefinition - the Phabricator Form. ...and fix a dumb bug in the query class so when you redirect to the view page / try to edit an existing NuanceSource you don't fatal.

Test Plan: played around with the edit form and it worked!

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7585