REGISTRAR: fixed workflow with group applications

- If user not set on application to group, we still can search for
  user by actor/extSource to match users which joined identities after
  application submission.
Merge pull request #336 from zlamalp/registrar

REGISTRAR: fixed workflow with group applications

- If user not set on application to group, we still can search for user by actor/extSource to match users which joined identities after application submission.