Modify combiner to allow setting of start/stop day range for combining events.

New Config Values:
	collector.combiner.days-ago-to-start
	collector.combiner.days-ago-to-end
	collector.combiner.days-ago-disabled
Obsolete:
	collector.combiner.min-days-back (replaced by: collector.combiner.days-ago-to-start)

Goal: Combiner instance to handle old events coming in late