Moved ConvertToEllipseAction from EditorKit to this class
Added conversion to Bezier curve
Added support for edit-with-center-fixed for parallelograms and ellipses
Added support for draw-with-center-fixed for parallelograms and ellipses
Added support for smooth-coeffs editing
Made CloseCurveAction undoable (bug fix)
Moved PEAction's dedicated to converting from EditorKit to PicSmoothPolygon
Added algorithms for SQUARE and CENTER_FIXED constraints
Added getDisplayName().
Added override for method remove() so as to work out bug when removing listeners.
