Changes to production cost calculation

Attentive facilitators had rightly pointed out to us that the production cost of finished goods, used to value inventory, was overlooking the production department's labor costs.

It's now done: the production cost takes production labor costs into account. These are indirect costs (like machine costs), and they are allocated in proportion to direct costs.

This change led us to update the various starting histories (simple, medium, expert). We made sure that the commercial and financial results of these new scenarios stay as close as possible to those of the previous histories.