Add picked step to customer shipment workflow

issue9634
review329071002

tests/scenario_account_stock_anglo_saxon.rst

@@ -245,6 +245,9 @@ Send 5 products::
     True
     >>> shipment.state
     'assigned'
+    >>> shipment.click('pick')
+    >>> shipment.state
+    'picked'
     >>> shipment.click('pack')
     >>> shipment.state
     'packed'