Registers the inputed walkthrough to the system.
        
        :param      walkthrough | <XWalkthrough>

def registerWalkthrough(self, walkthrough):
        """
        Registers the inputed walkthrough to the system.
        
        :param      walkthrough | <XWalkthrough>
        """
        if not walkthrough in self._walkthroughs:
            self._walkthroughs.append(walkthrough)