Get a list of namedtuples, one for each annotation.

def _init_dflt(self):
        """Get a list of namedtuples, one for each annotation."""
        nts = []
        ntobj = cx.namedtuple('ntanno', self.flds)
        for itemid, gos in self.id2gos.items():
            for goid in gos:
                nts.append(ntobj(DB_ID=itemid, GO_ID=goid))
        return nts