DepositionG4: add histogram diplaying the deposited energy per event

One item to discuss: Currently the axis range is adapted to the output_plots_scale / 2 * charge_creation_energy (factor of two because you always get two charges), which of course yields odd values for the axis range. Does this bother us? If yes, one could try to round that, introduce another config parameter or simply make it constant. I vote for keeping it as implemented now.