Add /universe endpoint

:construction: 

This is a first stab at the `/universe` API endpoint.

The JSON output does not include the following keys from the Berkshelf API output: `location_path`, `location_type`, `endpoint_priority`.  I wasn't sure what these keys would correspond to inside Supermarket, or if we even need them now.  The rest of the JSON should match, format-wise.

I included some basic caching around the query itself, and the view.  Adding or deleting a cookbook will invalidate the query cache, and refreshing the query cache will invalidate the view cache.

I'm definitely interested in feedback here before saying this is ready to go.

/cc @bcobb @tristanoneil @brettchalupa 
Can we leverage for SQL for this? If we are going to build this kind of structure, it seems like SQL would be much more performant than Ruby. I'm pretty sure PG has native JSON function: http://www.postgresql.org/docs/devel/static/functions-json.html.