Add New Relic.
Setup unicorn for Heroku.

Various instructions collected from:

* http://blog.codeship.io/2012/05/06/Unicorn-on-Heroku.html
* http://collectiveidea.com/blog/archives/2012/11/26/setup-a-high-volume-site-on-heroku-for-free/
Merge branch 'heroku_setup'