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 
Hmm...if I don't specify `canGrant` in a client update query, will it come through to here as `undefined`, be converted into `false`, and overwrite a previous value of `true` in the db?