Option to use old CPE error if charge exceeds one MIP

If useLegacyCPE is false and a positive value is given for maxChgOneMIP, ignore the merged status of the cluster and set the CPE error to the new value if chargePerCM is < maxChgOneMIP, else set the old value.  This cut is more robust against pileup than the sensor occupancy cut used to flag a cluster as merged.  We set the cut to -6000 in the config, where 6000 is a reasonable choice to turn on this selection.