[FIX] purchase_ux: do not update price when purchase is confirmed

Esto no solo mejora usabilidad si no que tmb resuelve problema de cancel remaining.
Aprovechamos a borrar los onchange que no son necesarios (ya tiene un depends por ser computado)
Ademas mejoramos un poco la funcion para tener menos "ifs"

closes #177

Signed-off-by: Juan José Scarafía <jjs@adhoc.com.ar>

purchase_ux/models/purchase_order_line.py

@@ -226,26 +226,26 @@ def action_add_all_to_invoice(self):
         for rec in self:
             rec.invoice_qty = (rec.qty_to_invoice + rec.invoice_qty)
 
-    @api.onchange('product_qty', 'product_uom')
     def _compute_price_unit_and_date_planned_and_name(self):
-        res = super()._compute_price_unit_and_date_planned_and_name()
-
-        for line in self:
-            if not line.product_id:
-                continue
-
-            # if price was not computed (not seller or seller price = 0.0), then
-            # use standar price
-            if not line.price_unit:
-                price_unit = line.with_company(line.company_id.id).product_id.standard_price
-                if (price_unit and line.currency_id != line.company_id.currency_id):
-                    price_unit = line.company_id.currency_id._convert(
-                        price_unit, line.currency_id,
-                        line.company_id,
-                        line.date_order or fields.Date.today())
-                if (price_unit and line.product_uom and line.product_id.uom_id != line.product_uom):
-                    price_unit = line.product_id.uom_id._compute_price(price_unit, line.product_uom)
-                line.price_unit = price_unit
+        """ Basicamente modificamos dos cosas:
+        a) si la compra esta confirmada y cambiamos cantidades u otro dato, que no se actualice ni precio,
+        ni descripcion ni nada. Esto, además de ser más lindo a nivel usabilidad resuelve problema de cancelar
+        remanente si el precio estaba modificado
+        b) if price was not computed (not seller or seller price = 0.0), then use standar price 
+        """
+        price_update_lines = self.filtered(lambda x: x.state not in ['purchase', 'done'])
+        res = super(PurchaseOrderLine, price_update_lines)._compute_price_unit_and_date_planned_and_name()
+
+        for line in price_update_lines.filtered(lambda x: x.product_id and not x.price_unit):
+            price_unit = line.with_company(line.company_id.id).product_id.standard_price
+            if (price_unit and line.currency_id != line.company_id.currency_id):
+                price_unit = line.company_id.currency_id._convert(
+                    price_unit, line.currency_id,
+                    line.company_id,
+                    line.date_order or fields.Date.today())
+            if (price_unit and line.product_uom and line.product_id.uom_id != line.product_uom):
+                price_unit = line.product_id.uom_id._compute_price(price_unit, line.product_uom)
+            line.price_unit = price_unit
         return res
 
     @api.model_create_multi