BibAuthorID: use defaultdict from containerutils
- Replaces local defaultdict backport with comprehensive one from containerutils.
Signed-off-by: Patrick Glauner <patrick.oliver.glauner@cern.ch>
Reviewed-by: Samuele Carli <samuele.carli@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>