states for faster
 retrieval. The states are updated whenever the model or the view state
 (translate, scale) changes. The scale and translate are honoured in the
 bounds.
 
 This class fires the following events:
 
 mxEvent.UNDO fires after the root was changed in setCurrentRoot. The
 <code>edit</code> property contains the mxUndoableEdit which contains the
 mxCurrentRootChange.
 
 mxEvent.SCALE_AND_TRANSLATE fires after the scale and transle have been
 changed in scaleAndTranslate. The <code>scale</code>,