Customer Delivery Date Selection on Checkout

A standard facility to allow uses to specify/request delivery dates on checkout. E.g. select from a calendar widget.

- Should factor in existing delivery rules. e.g. if no existing rules permit same day delivery, then the current day should be blocked on the date selector
- the business should be able to select whether weekends should/shouldn't be included as delivery date options on the calendar. If not, weekends should be blocked