* Most of the changes: align to the $ref object definition
(https://tools.ietf.org/html/draft-pbryan-zyp-json-ref-03#section-3)
that says that any attribute other than $ref be ignored.
* Remove extraneous leading ./ in $ref paths
* Fix an apparent typo in registration.yaml:
/account/password/msisdn/requestToken used a file from ../identity/*
instead of its c2s namesake.