TODO:
 - Callback on tree item select
 - Context menu with rename/copy/paste/duplicate
 - Delete with Undo/Redo support
 - Support for icons next to tree elements
 - Clicking on an already selectecd element starts rename 
   - Will likely need some kind of check to ignore double-clicks?

 Other:
 - "Ping" effect
 - Copy/Paste/Duplicate
   - This is more of a problem with actual copying of SceneObjects (It's not implemented). I should be able to serialize, and then de-serialize with a new parent as a form of copy.