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 
For completeness, it may be worth adding a sentence about how "fields not included in the request are left unchanged".  The below example makes this pretty obvious but it's nice to make these things explicit.