Allow the universe API endpoint to be filtered.

:fork_and_knife: 

When issuing a GET request to the /universe endpoint, allow the request to
filtered based upon specified cookbooks. One or more cookbooks can be requested
with a comma separated list.

Example:

`GET /universe?cookbooks=ruby,java,clojure`

Trello card: https://trello.com/c/pWTIRvzx

Closes #504.

![i-have-no-idea-what-im-doing-dog](https://cloud.githubusercontent.com/assets/928367/3769199/4c51ef1c-18df-11e4-8267-ed852b765756.jpg)

Two things to note:

1. Locally, using `IN` is consistently 2-4x faster than using a Regular Expression match. It also better represents the intent of this endpoint, in my opinion.
2. We need to sanitize user input, no matter what we do. [This](http://api.rubyonrails.org/classes/ActiveRecord/Sanitization/ClassMethods.html#method-i-sanitize_sql_hash_for_conditions) looks like a handy method.