Configure unicorn web server for heroku production deployment

Adds #eats, #drinks to Item model

* Fixes #66

* Adds test for default image

* Fixes typo in order spec

This has no impact on the development environment, but if you start `unicorn` on your local machine you'll see it set up for handling concurrent access workers.  `config.rb` is directly from the heroku knowledge base article.  It will also silence deploy errors about a missing `Procfile` for unicorn setup.