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 
This doc could use a few more details w.r.t form and purpose of the list, e.g. "An array of regexes; only users whose email matches one of these are allowed access to the admin API"