"Inherit" Unicorn Cookbook

...from
https://github.com/jsierles/peepcode-chef-recipes/tree/master/unicorn
Downgrade RubyGems be able to run `gem_package "bundler"`
Create Rails Cookbook

 * Install Nginx & Unicorn (from existing cookbooks)
 * define dependencies in metadata.rb
* create necessary directories
 * configure the Unicorn app server
 * config Nginx to serve this app as a Virtual Host + enable site