New generator with nexus hits as input

[jmunozv]

Up to date, nexus full simulations can be used for light studies in different geometries.

In the case we wanted to extend the use of full simulations for background studies, it would be necessary to implement a new generator. It would take as input the output hits of a previous nexus fast-simulation, and would generate the corresponding scintillation photons and ionization electrons.

The overall procedure would be:

1. Run a nexus fast-sim storing only those events with energy in the region of interest (Edep>2.4 MeV for instance), therefore discarding the majority of the events.

2. Run nexus full-sim with the new generator, taking as input the output of previous step.