Add Heroku SendGrid addon for mailing.

[scojasp]

This addon is apparently required for sending emails, which is required by our registration page.

https://elements.heroku.com/addons/sendgrid

Apparently, there is a free Starter package which allows 400 emails per day - this should be all that is required at the moment.

Can either do this via the website, or by using heroku addons:create sendgrid:starter from Josh's account.

[scojasp]

Leaving this here for later:

http://stackoverflow.com/questions/4114835/heroku-devise-missing-host-to-link-to-please-provide-host-parameter-or-set-d

[scojasp]

Saving these too: http://www.tutorialspoint.com/ruby/ruby_sending_email.htm http://jerodsanto.net/2009/02/a-simple-ruby-method-to-send-emai/