[IMP] sale_margin_delivered: Improve UI

Display % using the percentage widget and put all the new fields after the orginal margin fields from odoo. (prior to this change, the new fields were displayed among the margin fields from Odoo

sale_margin_delivered/views/sale_margin_delivered_view.xml

@@ -6,7 +6,7 @@
         <field name="model">sale.order</field>
         <field name="inherit_id" ref="sale_margin.sale_margin_sale_order_line_form" />
         <field name="arch" type="xml">
-            <xpath expr="//field[@name='margin']" position="after">
+            <xpath expr="//field[@name='margin_percent']" position="after">
                 <field
                     name="purchase_price_delivery"
                     string="Cost Price dlvd."
@@ -16,6 +16,8 @@
                     name="margin_delivered_percent"
                     string="Margin dlvd. (%)"
                     optional="hide"
+                    attrs="{'invisible': [('price_subtotal', '=', 0)]}"
+                    widget="percentage"
                 />
                 <field name="margin_delivered" string="Margin dlvd." optional="hide" />
             </xpath>