Keep task name for the new container if it is an empty leaf

This change implements the behaviour described in the analysis that you can
easily understand with the following example:

1) Initial scenario:
  * Task leaf "A" (0 hours)
  * Task leaf "B" (20 hours)
2) Indent task leaf "B"
3) Final scenario:
  * Task container "A" (20 hours)
    |- Task leaf "B" (20 hours)

FEA: ItEr76S13WBSSettingUpBehavior

libreplan-business/src/main/java/org/libreplan/business/orders/entities/OrderLine.java

@@ -144,7 +144,11 @@ public class OrderLine extends OrderElement {
     @Override
     public OrderLineGroup toContainer() {
         OrderLineGroup result = OrderLineGroup.create();
-        result.setName("new container");
+        String name = "new container";
+        if (isEmptyLeaf()) {
+            name = getName();
+        }
+        result.setName(name);
         return result;
     }