[8.0] pos_pricelist: Tax included prices

[jonerikceberio]

The pos_pricelist engine does not take into account the included taxes in the same way that the one in sale.order does: In sale/sale.py - product_id_change line 1206:

       price = self.pool.get('product.pricelist').price_get(cr, uid, [pricelist],

                product, qty or 1.0, partner_id, ctx)[pricelist]
        if price is False:
            warn_msg = _("Cannot find a pricelist line matching this product and quantity.\n"
                    "You have to change either the product, the quantity or the pricelist.")

            warning_msgs += _("No valid pricelist line found ! :") + warn_msg +"\n\n"
        else:
            price = self.pool['account.tax']._fix_tax_included_price(cr, uid, price, taxes, result['tax_id'])
            result.update({'price_unit': price})

So a method is called to ALWAYS take into account the included taxes if they are defined in the product. And this matches the impossibility to set a fiscal position that maps an included tax to an excluded one (although it can be easily overpassed by modifying the view).
The pos_pricelist engine does not take this into account and therefore the calculated price is different.

First steps to fix it in #138