Allow filtering

[grapoza]

Nodes can be searched using the getMatching method on the tree view, but it would be good to have a convenient way to filter the visibility of nodes. This would probably require:

• A way to set a node's visibility as part of the treeNodeSpec
• A method to go through the tree nodes (at the TreeView level) to set that visibility based on a provided method

Debouncing of the filtering would be outside the scope of the treeview and would be the responsibility of the caller.

[grapoza]

After giving it some though, this is really up to the user to decide what data to display, and to update the model used by the tree accordingly. Closing.