[Pharo-project] Dispatch morphic stepping from window back to model

See http://code.google.com/p/pharo/issues/list?cursor=2832 for details and please help to discuss if we really need this dispatching of #step methods from the view to the model and the no-op #step methods in Model and MCTool or if we can clean things up a little bit Thanks T. -- GRATIS für alle GMX-Mitglieder: Die maxdome Movie-FLAT! Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01