Create the API for viewing a single cookbook.

For example:

  GET /api/v1/cookbooks/apache

Note: this adds attributes to the Cookbook model. It does not handle the average
rating aspect of Cookbooks either.
Add indexes for cookbook names and versions.
Refactor the Cookbooks show action and view.

This removes the association logic and loops from the jbuilder template and
moves it into the CookbooksController. It creates a simpler view and a more
testable controller.
Remove the error_message method in the Api::V1Controller.
Properly format and expand upon CookbookVersion#to_param.
Remove spec_api_helper and create publish_version helper.