Add Extra cost on BOM

Split the method to write standard_price on product in 2: one to compute the unit price of the MO, another one to update the standard_price on the product

mrp_average_cost/mrp_view.xml

@@ -14,6 +14,9 @@
     <field name="inherit_id" ref="mrp.mrp_bom_form_view"/>
     <field name="arch" type="xml">
         <xpath expr="//div[@groups='mrp.group_mrp_routings']" position="after">
+            <field name="extra_cost" widget="monetary"
+                options="{'currency_field': 'company_currency_id'}"/>
+            <field name="company_currency_id" invisible="1"/>
             <label for="labour_time"/>
             <div name="labour_time">
                 <field name="labour_time" class="oe_inline"/>