[EdgeFigure] Added support for selectively disabling rendering

Simply calling IFigure.setVisible also seems to disable clipping, which is
not what we want at all. This commit also changes outline rendering a bit
to fix the redrawing bug mentioned in the last commit message
[EdgePart] Use the new setRender method to toggle the figure's visibility
[icons] Added an icon for the new edge-display-toggling action
[RedActions] Added a new class for creating some Big Red-specific actions

All of the GEF viewer property toggle actions are now implemented here
[editors] Use RedActions to create the viewer property toggle actions
[rule] Added the toolbar button for toggling edge display