Purchase Variant Configurator On Confirm

This module extends the purchase variant configurator so that purchase orders can be prepared with product templates and only generate the real product variants at confirmation time.

• On a purchase order line you can now select a product template (product_tmpl_id) in addition to the usual product field. The product field is no longer mandatory on purchase order lines.
• When you confirm the purchase order, any line that has a template but no product automatically creates the needed variant before the order is confirmed, so stock moves are created for the right product.
• The same automatic variant creation happens if a line is created directly on an already confirmed purchase order.
• When you duplicate a purchase order, lines without a product get their planned date recalculated using the supplier information, so the copy stays consistent.
• Selecting a template fills in the line description and purchase description from the template, and looks up the correct supplier price list for that template.
• Database checks ensure accountable lines still have the required information (template or product, unit of measure, planned date) and that non-accountable lines (section/note lines) do not carry product values.

The module touches purchase.order, purchase.order.line, product.template, product.product and product.supplierinfo. It adds the template field to the purchase order form view.