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 
Offtopic, but speaking of SQL, any plans to move from SQL queries to Stored Procs, similar to https://github.com/mozilla/fxa-auth-db-server/issues/81?