Fixed Participation.matches_filter? method to utilize .nil? checks instead of .present?.
Added delinquent_cutoff_time to constants for temporary use.
Added StandingCalculation.time_online method to pair with time_in_raid method, allowing simple calculation of time within the raid (default to only within cutoff period).  Closes #37
Fixed issue in StandingCalculation.calculate[:deliquent_loss] logic, which was causing cutoff_time_offline value to be far larger for comparison than intended.