Rails 4.1 Mailer Preview
see http://edgeguides.rubyonrails.org/4_1_release_notes.html#action-mailer-previews
https://app.asana.com/0/11169835259596/11879617411591
Merge pull request #6 from UW-Advanced-Rails-2014/email-previews

Rails 4.1 Mailer Preview