[MCC-140729] Feature/update

Merge after #14

Adds more drd attributes from the descriptor doc, an udpate method, and a happy case update spec.  Also refactors some specs to use a new hale_url_for helper to make things pretty.  I decided to make the udpate 303 to the self link, I think it will be useful for testing following redirects in farscape.

NB: I change destroyed to destroyed_status, as rails has pretty firmly claimed ``` destroyed ```on a model.

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