Display the code for all products in the tree view

A product might have an optional code. This code is currently not displayed in
the product tree view.

Adding the product code as separate field before the product name to the
product tree view to allow users to search for a product by its code.

issue5828

review32491002

product.xml

@@ -91,7 +91,7 @@ this repository contains the full copyright notices and license terms. -->
             <field name="type" eval="None"/>
             <field name="inherit" ref="template_view_tree"/>
             <field name="priority" eval="10"/>
-            <field name="name"></field>
+            <field name="name">product_tree</field>
         </record>
 
         <record model="ir.ui.view" id="product_view_tree_simple">

view/product_tree.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
+this repository contains the full copyright notices and license terms. -->
+<data>
+    <xpath expr="/tree/field[@name='name']" position="before">
+        <field name="code"/>
+    </xpath>
+</data>