code: public LienzoPanel add(final Layer layer, final Layer... layers)
      {
          add(layer);
  
          for (final Layer node : layers)
          {
              add(node);
          }
          return this;
      }
docs: Adds a layer to the {@link LienzoPanel}.
  It should be noted that this action will cause a {@link Layer} draw operation, painting all children in the Layer.
  
  @param layer
  @return