Save publishers master list in repository.

[dsummersl]

The list of publishers is currently downloaded from https://www.citygram.org/publishers.json, and then inserted into the database when you run bundle exec rake publishers:download. Unfortunately, the list on the internet isn't complete, and appears to change over time, which makes it impossible to setup reproducible environments. Save this file in the repository, and modify publishers.rake to build the database from the local file.