Users can send pitch emails to journalists

UPDATE: By passing journalist object to mailer (instead of just journalist email address), pitch emails can now include the journalist's name e.g. ("Hi Fred").

Trello card: https://trello.com/c/rtMxACiY/56-send-pitch-emails

![email](https://cloud.githubusercontent.com/assets/4560985/5252379/231d97e4-796b-11e4-9ca1-a6e224eca4be.gif)