'Registers a :class:`~horizon.workflows.Step` with the workflow.'

@classmethod
def register(cls, step_class):

    if (not inspect.isclass(step_class)):
        raise ValueError('Only    classes    may    be    registered.')
    elif (not issubclass(step_class, cls._registerable_class)):
        raise ValueError(('Only    %s    classes    or    subclasses    may    be    registered.' % cls._registerable_class.__name__))
    if (step_class in cls._cls_registry):
        return False
    else:
        cls._cls_registry.add(step_class)
        return True
