Up to know, order builders were mostly used having in mind the idea of
deleting all previously created automated orders.

This way was mostly requesting to run generated delivery builder only
once per night, assuming there is no users working at that time.

So to allows running very often (many times a day) generated delivery
builders, allow them to update existing deliveries. This way :
- automated deliveries could be much more up to date
- there is no need to delete everything
- this generate few activities, there is no need of a long calculation
  to update everything

Also, the stock optimization was using dates with a precision of one
full day. Generic code must support much better precision.