Implements Client Management Endpoints

We already had the R of CRUD, this adds the other 3. The 3 new endpoints require an oauth token with the scope `oauth`. Yo dawg, I heard you like oauth?

@rfk r?
@vladikoff you should take a look and see if there's something I've forgotten that the console will need.

fixes #60 
Both the constant names and the actual string values here aren't particularly enlightening to me, and it's not clear how we extend this naming convention to add an second auth strategy, like request signing.