Creates an order and generates an UUID as well as a shortID which can be used to retrieve the order. Any token (public or private) can be used to create an order. NOTE - 'items' has been deprecated and replaced by 'cart'. In order to maintain backwards compatibility, items will still be populated with incoming data. However it will converted to the correct format and also saved in 'cart'. If the data is in incorrect format, it will not be touched. Please ensure that 'cart' field is used instead of 'items' field.