+ Added a warning message box if, while saving a scene, one or more referenced nodes don't have properly assigned handles
+ Added a warning message box if, while loading a scene, one or more nodes don't have properly assigned handles. These nodes are then defaulted to root scene nodes and the rest of the scene (and ZK data) loads normally.

* Fixed nodes being re-sorted by name after each rename in tree view
* Fixed hanging and unpredictable selections when using sorting by name in tree view