added gem acts_as_shopping_cart
added models for shopping_cart & shopping_cart_item
added basic shopping cart functions (add item, remove item, clear cart)
added view for cart
added jquery to update cart count and update current page when adding
item
added (some) logic to make sure items don't get added multiple times and
to prevent sold items from being added
set sales tax to 0% (for now)
moved parts of views for products/show products/index home to partials
cleaned up product_list partial
fixed broken sti_product_path
bring branch current