Enhanced support for bundles in checkout

added support for "build your own" bundles from FoxSell Bundles

added optional setting: during multi-recipient checkout, any line item properties from cart items will be carried through to payment and child orders

added an offset days setting to adjust first available local delivery date in checkout. Set this in the Zapiet or Bird widget in Send To Many > Settings > Checkout > Recipient Fields

updated the "Multi Checkout Button" to automatically mimic the style and positioning of the Add to Cart button on cart pages