Add confirmation email

Hi @davidtlee, we'll need to (1) add some ENV variables to the heroku production environment and (2) change the email address/domain the email (so that we're sending from www.crowdconsensus.com or whatever and (3) finalize the text of the email (it's pretty simple right now). Other than that, this is working in development!

I don't have access to heroku - if you add me as a collaborator on the account (my username is jyl702@gmail.com), I can add the right ENV variables (check out setup_mail.rb to see the var names). Or feel free to add them yourself - whatever you think is best!