slapos_accounting: set the source_project on the open sale order

master/bt5/slapos_accounting/SkinTemplateItem/portal_skins/slapos_accounting/InstanceTree_requestUpdateOpenSaleOrder.py

@@ -28,6 +28,7 @@ def newOpenOrder():
     destination_decision=person.getRelativeUrl(),
     title="%s SlapOS Subscription" % person.getTitle(),
     ledger_value=portal.portal_categories.ledger.automated,
+    source_project_value=instance_tree.getFollowUpValue(),
   )
 
   new_open_sale_order.order(activate_kw=activate_kw)