adds Partner column to product sales report
  * adds new Partner model, which :has_many products
  * updates admin/product edit view so that a partner can be associated
    with a given product
  * adds a rake task to populate the DB with the default list of
    Partners
      * stored in config/partners.yml in reservebar.com repo
      * skips over any entries that are already in the DB
  * adds Partner column to product sales report