Report additional attributes that come from the OAuth server, as per gui...

...deline https://github.com/intridea/omniauth/wiki/Auth-Hash-Schema

Specifically: Report Heroku's user_id in uid attribute; the token_type in the 'credentials' hash, and the access_token params in 'extra' => 'raw_info'
This was needed, to uniquely identify the user on the client app.