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 
This `client_id` type definition is duplicated in several places, consider refactoring it into a shared definition.  e.g. auth-server does this a bit in `/routes/validators.js`.