Updated editor for choosing delivery methods in the checkout form.

Updated editor for choosing delivery methods in the checkout form. Added the ability to additionally specify a fixed shipping cost. Added the ability to use conditions to display the delivery method depending on the order amount.

Added "Purchase price" for varieties.
Added XML / YML upload for MarketPlace Rozetka and Yandex Market with product characteristics.
Added instructions for creating a pop-up block with the contents of the shopping cart.