HowTo
   
    Select a single tree node (in picking mode), then press the Collapse button to
    hide the children of that node. Select again and press Expand to restore the children.
	
	    
Mouse listeners:
    
    
Picking Mode:
	
	-  MouseButtonOne press on a Vertex or Edge to select it
	
-  MouseButtonOne+Shift press on a Vertex or Edge to add or toggle selection
	
-  MouseButtonOne+drag on a Vertex to move all selected vertices
	
-  MouseButtonOne+drag to select Vertices in a rectangle
	
-  MouseButtonOne+Shift+drag to add to selection with Vertices in a rectangle
	
	
TransformingMode:
	
	-  MouseButtonOne+drag to translate the display
	
-  MouseButtonOne+Shift+drag to rotate the display
	
-  MouseButtonOne+ctrl(or Command)+drag to shear the display
	
	
Both Modes:
	
	-  MouseWheel to scale. When scale < 1, view is scaled. When scale > 1, layout is scaled.