Return overlay as a dictionary.

        :param overlay_name: name of the overlay
        :returns: overlay as a dictionary

def get_overlay(self, overlay_name):
        """Return overlay as a dictionary.

        :param overlay_name: name of the overlay
        :returns: overlay as a dictionary
        """
        url = self.http_manifest["overlays"][overlay_name]
        return self._get_json_from_url(url)