add. UMPRegInput class to handle users whose reg date falls within the metric input dates.
add. UMPRegInput class to handle users whose reg date falls within the metric input dates.

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