Resend option for confirmation emails

[ajdlinux]

If for some reason Patchwork fails to send a confirmation email to a new user or a user adding a new email address, we don't currently have an easy way to trigger a resend.

This should be fairly easy, we just need to factor out the code that currently sends the confirmation emails, and add some extra views to trigger a resend.

[stephenfin]

Had a quick look at this this morning. We probably also need to work around this issue since there's currently no indication given that the user is inactive when attempting to log in.