Make a first validation test on the basis of radio-emission simulation

@Nikos has some nice scripts producing radio-emission plots for standard showers. We should evolve these into a first validation test (comparing energy fluences, signal polarisation, radiation energy, Xmax, total energy deposit, ...), say to be run on each merge. It could then suit as a basis for adding further validation tests. I hope that @lukas can hope to make this happen.