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 
I suggest just `POST /v1/client` for this endpoint to be slightly more restful, but will not put up even a token resistance if you prefer to keep the `register` suffix...