Attachment / Upload email links now throw 404 if not logged in (SSO)

[wesochuck (Wes Osborn)]

Still seeing this on v1.8.0.beta4 +72. Wondering if something similar to what was done over here could be put in place for upload links:

`/my/preferences` should not take you to a 404 page

We link http://sitename/my/preferences in a bunch of places in emails with text similar to: "To change your preferences click: http://sitename/my/preferences. If a user is not logged in clicking on that link takes you to a 404, this can be very confusing, especially for mailing list migrations. Instead we should have a special /my/preferences page for anon that explains they are not logged in and provides instructions on how to log in. cc @eviltrout