@classmethod
def registerAddonModule(cls, module):
    """
        Registers a module to use to import addon subclasses from.
        
        :param      module | <str> || <module>
        """
    prop = '_{0}__addon_modules'.format(cls.__name__)
    mods = getattr(cls, prop, set())
    mods.add(module)
    setattr(cls, prop, mods)
