Add account confirmation emails for email registrations.

[mattlindsey]

Registration by email is currently disabled in production because otherwise hundreds of fake/spam accounts get generated monthly.

Add the requirement to 'confirm' email accounts by clicking on a link in a confirmation email. The devise gem should have this feature. Then we can re-enable email account registration on production (in production.yaml).

[wordhouse66]

Hello Matt. I would like to take this on if it is ok

[mattlindsey]

Closing this because it's probably not a good idea to re-enable email registration without a way to avoid spam accounts.