Changed UnitUtils.ShouldInterrupt(unit) to return the closest target if there are multiple enemy units casting.
Fixed Glacius' Ice Imprisonment AbilityInfo: it can NOT interrupt magic immune targets.
Updated AbilityInfo to replace IsSingleTarget with TargetType which is more universal.
Updated UnitUtils.GetThreat to include a debug parameter rather then have it set in the UnitUtils object.
Added parameter bIncludePorts to ShouldInterrupt to determine if we want to try to stop ports too.
Added UnitUtils.IsMagicImmune(unit) for checking if the target unit is magic immune.
Added UnitUtils.HasNullStoneEffect(unit) for checking if the target has a null stone effect active that would nullify our spell.