[orders] Group basket by collection

When placing an order, the basket will automatically be split in as many orders as necessary, depending on the showroom settings. There are two types of order split: by collection (eg. one order per collection) or by inventory mode (eg. per preorder, immediate in-stock, incoming in-stock).

To let users preview the order split, basket views now all display ordered products grouped by collection or by inventory mode, depending on the active split settings. This affects the Cart screen (as a buyer), and the Set quantities and Order review screens of the sales tools.

Preview order split by collection