'converted( self, trans, dataset_id, ext, **kwargs )
* GET /api/datasets/{dataset_id}/converted/{ext}
return information about datasets made by converting this dataset
to a new format
:type   dataset_id: str
:param  dataset_id: the encoded id of the original HDA to check
:type   ext:        str
:param  ext:        file extension of the target format or None.
If there is no existing converted dataset for the format in `ext`,
one will be created.
If `ext` is None, a dictionary will be returned of the form
{ <converted extension> : <converted id>, ... } containing all the
*existing* converted datasets.
..note: `view` and `keys` are also available to control the serialization
of individual datasets. They have no effect when `ext` is None.
:rtype:     dict
:returns:   dictionary containing detailed HDA information
or (if `ext` is None) an extension->dataset_id map'

@web._future_expose_api_anonymous
def converted(self, trans, dataset_id, ext, **kwargs):

    decoded_id = self.decode_id(dataset_id)
    hda = self.hda_manager.get_accessible(decoded_id, trans.user)
    if ext:
        converted = self._get_or_create_converted(trans, hda, ext, **kwargs)
        return self.hda_serializer.serialize_to_view(converted, user=trans.user, trans=trans, **self._parse_serialization_params(kwargs, 'detailed'))
    return self.hda_serializer.serialize_converted_datasets(hda, 'converted')
