Signups now must to click button to confirm email, fixes #1468

[prioux]

This should be easy to review.

When testing, remember that your dev environment doesn't actually send emails, but you can find the email's content in your RAILS logs.

YOu'll be able to find the URL of the confirm page, just post it in a incognito window.

You can also reset the 'confirmed' status in the console for multiple rounds of trials with

s = Signup.find(23) # adjust number
s.confirmed = false
s.save