Email producers with order/delivery instructions #275

Would be great to get a review of this as a sanity check.
Should `first_producer` actually be `first_distributor`? Also, `@distribution_date` looks a touch fragile. If there are different pickup times for the hubs in an order cycle, this will mean that the email will show the first one, which might be several days after the food is needed elsewhere.

It'd be great to show the earliest pickup time, but the pickup time is stored as a (not necessarily parsable) string, so we can't do that. We could show all unique times, which might be a little better, though it could be messy and confusing, too. I don't know an easy answer at this stage, what are your thoughts?