Checking user.email is not ok because allauth allows multiple
addresses per user but grants access if any of them is verified.

-> we need to ensure that the matched address is verified


Thus a (non-admin) user can import a webapp only if the two
conditions are met:
- the user is allowed to create webapps (verified by IsProviderMixin)
- the user has a verified email address that matches the owner
  address of the imported webapp