setImages(imageObj, imageObjAlt) {
    if (imageObjAlt && this.selected) {
      this.imageObj = imageObjAlt;
      this.imageObjAlt = imageObj;
    } else {
      this.imageObj = imageObj;
      this.imageObjAlt = imageObjAlt;
    }
  }
Set the images for this node.

The images can be updated after the initial setting of options;
therefore, this method needs to be reentrant.

For correct working in error cases, it is necessary to properly set
field 'nodes.brokenImage' in the options.
@param {Image} imageObj  required; main image to show for this node
@param {Image|undefined} imageObjAlt optional; image to show when node is selected