adds feature to allow admin to see retailer pricing for each product
* adds a new page, accessed via the sidebar when editing a product
* that page also include a link to allow admins to download a copy of
  the retailer pricing for a given product
Merge pull request #27 from ReserveBar1/list-all-retailer-pricing-for-given-sku

adds feature to allow admin to see retailer pricing for each product