function setOrGetLinksVisible(newValue) {
    if (newValue === undefined) {
      return linksVisible;
    }

    if (newValue) {
      scene.add(linkMesh);
    } else {
      scene.remove(linkMesh);
    }

    linksVisible = newValue;
    return linksVisible;
  }
Gets or sets links visibility. If you pass truthy argument
sets visibility to that value. Otherwise returns current visibility