Feature request: TreeState and expandedNodes

[.:lexx:.]

It will be perfect if developer can have access to expandedNodes Set in TreeState. This will help to restore expansion state after dynamic model change.

Example:

 public void remove() {
 log.info("Remove");
 root.remove(0);
 rebuild();
 }

 private void rebuild() {
 uiRoot = builder.build(root);
 if (tree != null) {
 TreeState treeState = ((TreeState) tree.getComponentState());
 List<TreeRowKey> rowsToExpand = new ArrayList(treeState.getExpandedNodes());

 tree.resetDataModel();

 for (TreeRowKey key : rowsToExpand) {
 try {
 tree.queueNodeExpand(key);
 } catch (IOException e) {
 log.error("Error", e);
 }
 }
 }
 }