fix SMTP notification not sent

[sdebruyn]

Fixes #898 #911

Before attacking the tests, let me know what you think of this approach.

Raising the exception will always exit the current code path in authentication.py

[AndreyNikiforov]

IIUC you are trying solve two problems: a) that smtp notification is terminating the app when webui is enabled b) smtp notification is not supported for mfa requests. The solution is to send smtp notification on password/mfa requests while still keeping icloudpd with webui working to enter those credentials. Is the scope for initial auth only or re-auth as well?

[sdebruyn]

As long as the authenticator is called, it will also trigger the callback again. And indeed, it keeps it from exiting after sending the email. I also needed this to work better for #1008