[FIX] TreeViewPlugin sortNodes fix

[xeolabs]

This PR fixes spatial sorting of TreeViewPlugin nodes that represent IfcBuildingStorey elements.

Sorting is disabled by default, but can be enabled like this:

    new TreeViewPlugin(viewer, {
        containerElement: document.getElementById("treeViewContainer"),
        autoExpandDepth: 3, // Initially expand tree three storeys deep
        hierarchy: "containment",
        sortNodes: true
    });
    ````