code: private boolean closeAllWindows(SwingFrame navigationFrameView) {
  		// Die umgekehrte Reihenfolge fühlt sich beim Schliessen natürlicher an
  		for (int i = navigationFrames.size()-1; i>= 0; i--) {
  			SwingFrame frameView = navigationFrames.get(i);
  			if (!frameView.tryToCloseWindow()) return false;
  			removeNavigationFrameView(frameView);
  		}
  		return true;
  	}
docs: Tries to close all windows. Stops at first failed attempt.
  
  @param navigationFrameView used as parent of question dialogs
  @return true if all windows are closed