Allow SMTP Authentication to be nil

[20wildmanj]

Your environment
Carnegie Mellon Autolab Instance

From Chaskiel: "The new email sending config interface does not allow using an smtp server that doesn't require authentication. It should be possible to set authentication to nil."

Steps To Reproduce
Steps to reproduce the behavior:

1. Go to 'Configure Autolab'
2. See that there exist multiple authentication options but no option to not have authentication

Expected behavior

There should be an option to not have authentication