Separate tree and branch names for data and simulations for plotter/fitter
Currently the provided tree and branch names will be used to open all input files - both data and simulations. However I believe one use-case for the program would be to compare some experimental data with the raw, untreated output of sim3a, which is not currently possible, since they'd probably use different tree/branch names.
To fix this, we'd have to allow using one set of names for experimental data, and another for simulations.