FR: Order-level snapshot

[jamiepittock]

At the moment, if a user updates their email address, Commerce resaves all their past orders and updates the order email.

That's fine, although there is an argument for not doing that - but it's a different discussion. However, in our case it would be useful to have a snapshot of the order when it was completed, so we always know the original email address.

I guess this feature request could be wrapped up in others asking for order history and audit trails but they seem much more complex to implement, whereas a simple order-level snapshot could be relatively straight-forward.

The email address is the one thing that can be changed on an order by the customer after completion and it's out of our control.