Add /universe endpoint

:fork_and_knife: 

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 
Given that we're phasing out Magiconf for dotenv, this should be `ENV['HOST']`.