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 
Not really, no. It started as the idea of "this client can automatically have permission (don't prompt user)". Such as, the Marketplace could automatically have your email and avatar.

For now, all clients are whitelisted, and the value isn't used (other than a check in `/v1/authorization` that throws a 500 if not whitelisted.)