Feature add singles for scifi studies
Adds singles for scifi studies. Steering files of the form:
from DDSim.DD4hepSimulation import DD4hepSimulation
from g4units import mm, GeV, MeV, degree
SIM = DD4hepSimulation()
SIM.gun.energy = 100*MeV
SIM.gun.particle = "gamma"
SIM.gun.position = (0.0, 0.0, 0.0)
SIM.gun.etaMin = 0.0
SIM.gun.etaMax = 0.0