Add.  aggregator to compute average for a group of editors.
Add.  aggregator to compute average for a group of editors.

rfaulkner/wikipedia_user_metrics,wikimedia/analytics-user-metrics,wikimedia/user_metrics,wikimedia/analytics-user-metrics,wikimedia/analytics-user-metrics,rfaulkner/wikipedia_user_metrics,wikimedia/user_metrics,rfaulkner/wikipedia_user_metrics,wikimedia/user_metrics