Never store the hawkCredentials.id directly.
On registration store an encrypted userId per hawkSession.
Fix req.token became req/callUrlData.
Add the name of the caller to the GET /calls endpoint.
decrypt/encrypt should throw an error when passed a null string
Remove the hawk.buildId feature
Move the tests for hmac in a dedicated file
s/hawkHmacId/hawkIdHmac
s/{get,set}UserId/{get,set}HawkUserId
@ametaireau review
Sync with master
Merge pull request #133 from mozilla-services/1032253-encrypt-userId

Bug 1025881 — Store validated userId from certificate during the registration phase.