Started to split CheckoutForm into PaymentForm
Switched stepped checkout setup to use yaml
As found in #214
Tidied ShopConfig.
Make CheckoutStep_Summay use PaymentForm instead of CheckoutForm
Updated SteppedCheckoutPage.ss template to use Cart template, as Cart_ReadOnly is now gone.
Added CheckoutPage_payment template for independently styling the on-site payment entry page.
FIX: use correct config variables in OrderActionsForm …remove redundant config fields from OrderManipulation.
Added some tests for CheckoutPage / OrderActionsForm