Add option to symmetrize shapes

Release notes

Symmetrize shapes with one-sided bins in ActionProcessSystematics

Details

Specify systematics for which to symmetrize one-sided bins with histoSys.systsToSymmetrizeBins. An additional option is implemented in ActionProcessSystematics to prune shapes that stand out with very large variations in some bins. This can be done with tags histoSys.systsToCutOff, histoSys.systsCutOffHigh, histoSys.systsCutOffLow.