Query by cookbook name in a consistent manner

:fork_and_knife: 

This addresses two bugs found while running imports locally:

1. Querying cookbooks by case-sensitive name in the cookbook versions API caused 404s for some cookbooks.
2. Querying cookbooks by case-sensitive name when publishing a new version of a cookbook would occasionally miss cookbook dependencies whose names were specified in a different case than the cookbook record.

Note: We could continue to query by LOWER(name), but Rails's Ruby schema language does not preserve Postgres expression indices, and building in support for such things does not seem like a high priority at the moment. SQL schema dumping is not a viable option, either.