#485 - Major refactor of Checkout Page - created a OnePageCheckoutProcessor that sets up the vars necessary for implementation. Added a Null Payment Gateway Hosted service to mock flows like PayPal Express Checkout and moving the completeCheckoutOnCallback flag from the Configuration Service to the DTO, this is bc that should be determined by when the call is made (e.g. on the cart page vs the checkout page when shipping has already been applied)