add systematics aware filter reporters

Essentially this is trying to stick as much as possible with the interface from regular filter reporters, but adds an intermediate combiner class that combines the decisions for individual systematics into an overall decision for the event, i.e. it will set the filter-passed flag to false, if the filter decision is false for all systematics.

For reporting I just moved over all the functionality that was previously in EventSelectionByObjectFlagAlg, which is the only systematics-aware filter algorithm we have right now. I also updated that algorithm to use the new filter reporters. At some point we should probably revamp the actual reporting, but for now I'm just trying to get the reporter interface into place.

Let me cc the usual suspects: @akraszna @alister @lheinric @jburr @tadej @mmuskinj