code: def list(self, external_id=None):
          
          response = self._get('base')
          return [VoicebaseMedia(o, self.api) for o in response['media']]
docs: Retrieve from the media colection.
          HTTP GET on /media
          :param external_id: A unique identifier in an external system, set in metadata on POST.
          :return: list(VoicebaseMedia)