Add alternative rho computation options, and put these in JETM1

We desire to test several definitions of the definition of the pile-up energy density to try to reduce the dependence of the calculation on the hard scatter event topology which then becomes an uncertainty on the JES. We have created two alternative definitions and added them to JETM1. Further details can be seen in talks given in JES/JER and JSV JetEtmiss meetings: https://indico.cern.ch/event/784289/ https://indico.cern.ch/event/814856/