Feature request - Implement new eCommerce features

This ticket attempts to consolidate (and help prioritize) ecommerce tickets #729, #732, #733, #734, #736, #778, #974

• ecommerce setup wizard #729
• quick checkout #733, with the idea of optionally going straight to the cart, or simply adding the item to the cart and remaining in the product catalog/index, and maybe event straight to checkout
• more event registration options #778, should include quantity and early registration discounts and allow dealing with 'half-purchased' events which have been added to the cart, but not checked out yet (since the registrants are already in the table), maybe consider an 'e-ticket' type of invoice?
• 'digital' purchases #736, would be nice to grant 'permissions' to download based on a purchase
• add 'comments' (reviews) to products #732, add comments (reviews) in addition to ratings and maybe make the rating apply to each comment
• add a 'free' payment calculator #734, with the intent that if there is no cost for the items, we should bypass the payment part
• merge cart configuration into store configuration #974, not sure why we don't add the two specific cart configuration settings with the rest of the cart configuration settings in the storeController