Order acknowledgements

[niallct]

A mechanism to record whether or not a producer has confirmed they can supply an order. (refinement: when they did so, and email/phone/verbal)

Then a report on unconfirmed orders, so that producers can be chased up, and/or the order considered tentative.

This is a tool for managing orders rather than casks, which should remain `virtual'.

Needs thought on whether/how to capture changes between order and arrival, and how arrived status interacts with order-confirmed.