Comparative tabulation csv download

Adds comptab csv download to the admin interface. This does not cover any extra functionality, such as "converting countries".

Additionally, both the comptab and the raw shipment format now support multilingual column names (the Spanish and French names are not set though; this is more relevant for the public interface). The way to test it is to pass e.g. locale=es in the download url. 

need to run rake db:migrate to create the view which powers the report.