Add optional column on tree view

issue10989
review374321002

view/shop_list.xml

@@ -2,8 +2,8 @@
 <!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
 this repository contains the full copyright notices and license terms. -->
 <tree>
-    <field name="name"/>
-    <field name="currency"/>
-    <field name="type"/>
-    <field name="company"/>
+    <field name="company" expand="1" optional="1"/>
+    <field name="name" expand="2"/>
+    <field name="currency" optional="1"/>
+    <field name="type" optional="0"/>
 </tree>