delete price property from Sale.
scaffold SaleCategory.
add SaleCategory into settings.
Revert "delete price property from Sale."

This reverts commit d8a41f0ab758fad1bad4fd02307340f23d16443c.
delete price and genre_id. add price_id and sale_category_id into Sale.
Merge pull request #5 from aratana/feature/create-sale-category

Feature/create sale category