add. method get_registration_dates to handle pulling registration data for users.
add. method get_registration_dates to handle pulling registration data for users.

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