#195 Tooltips are sometimes incorrect for edges
Tooltips sometimes display incorrectly for edges. If there are multiple edges close together, sometimes the wrong one gets displayed or a tooltip for an edge might never get displayed and other times the tooltip is displayed despite the mouse not hovering over anything.
When obtaining the tooltip for edges in VisualizationViewer.getToolTipText, it transforms the mouse location into the view coordinates and passes it to the edge pick support to determine which edge is at the mouse location. However, ShapePickSupport will also transform the coordinates into the view coordinates and return the edge at the transformed coordinates. I've worked around this by subclassing VisualizationViewer to override the getToolTipText method to NOT transform the mouse point.
