Add the external code when a whole order is imported as subcontrated task.

Although this operation is not permit by the interfaz, this one give us
clarity on the code. All subcontrated task have got the external code filled.

FEA: ItEr75S28CustomerIncommingCommunicationsLists

libreplan-webapp/src/main/java/org/libreplan/ws/subcontract/impl/SubcontractServiceREST.java

@@ -195,6 +195,7 @@ public class SubcontractServiceREST implements ISubcontractService {
             order = (Order) orderElement;
             order.setVersionForScenario(current, version);
             order.useSchedulingDataFor(version);
+            order.setExternalCode(order.getCode());
         } else {
             order = wrapInOrder(current, version,
                     orderElement);