Desired delivery date or periods

[AndreiMaz]

In some cases customers would prefer to choose delivery date (or periods) during checkout (after a shipping method or option is chosen).

There's no need to implement this option for online shipping rate providers. But it would be helpful for offline shipping providers.

Let's discuss the implemention. But looks like the best way to go will be extending the "ShippingOption" class with new properties. They will indicate whether delivery dates (or periods) are available for choosing. If not, then customer won't be able to choose delivery date for this shipping option