Add statement to editable line view

It is needed to have the statement_state field computed correctly.

issue6507
review42381002

view/statement_line_tree_editable.xml

@@ -2,6 +2,7 @@
 <!-- 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 editable="bottom" sequence="sequence">
+    <field name="statement"/>
     <field name="number"/>
     <field name="date"/>
     <field name="amount" sum="Amount"/>