Work in progress, ref #9

  * user has no email
  * we have to get the email out of openid, because email is unique
Added correct axschema and handling method to retrieve email attribute from openID provider, ref #9
remove uniqueness from email field, add uniqueness to identity_url field, ref #9
Merge remote-tracking branch 'origin/dev' into Biber/feature/authentication
Merge branch 'Biber/feature/authentication' into dev