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'm not a fan either. It would require an `ALTER TABLE`.

The logic here is that from config, the property is `hashedSecret`, and clients pulled from the database, since the column is `secret`, have the property `secret`.