text: Title: NotConfigured logging breaks when the component is added by class object
  Body: As the log message for components that raise `NotConfigured` with a message assumes `clsname` is an import path string, it raises an AttributeError when it's a class instance. https://github.com/scrapy/scrapy/blob/bddbbc522aef00dc150e479e6288041cee2e95c9/scrapy/middleware.py#L49