GraphicalEditPart is a NotificationListener that is
why it implements the Notifychange, This method we had a generic event
handling optimization code that should be applicable to all edit parts. for example if the edit part was not active it will
just return without doing any thing so, clients should override this method only if they
like to add more generic filtering for their edit parts hierarchy the other method, handleNotificationEvent will be
called if the Graphical edit part decided it is possible to handle events
(this is determined by the notifychanged method), this is the method clients
should override to add specialized event handling to their edit parts