Create a new IndividualAggregator.
Clients should connect to the IndividualAggregator.individuals_changed signal (or the IndividualAggregator.individuals_changed_detailed signal), then call IndividualAggregator.prepare to load the backends and start aggregating individuals.
An example of how to set up an IndividualAggregator:
IndividualAggregator agg = new IndividualAggregator ();
agg.individuals_changed_detailed.connect (individuals_changed_cb);
agg.prepare ();