Modify API to return info about auto-awarded STEAM badges

POST /v2/user/badge/\<shortname\> and POST /v2/claim will now include an autoAwardedBadges array in their response, which contains the shortnames of any auto-awarded steam badges that resulted from the badge award.

This addresses https://github.com/mozilla/openbadger/issues/191 and will support https://github.com/mozilla/openbadger/issues/197.