Energy-based switch process

This new process encapsulates two InteractionProcesses (or multiple of them in a ProcessSequence) and depending on the projectile energy relative to a constant threshold energy, selects one or the other.

Use case:

auto const sibyllSequence = sibyll << sibyllNuclear;
SwitchProcess switch(urqmd, sibyllSequence, 55_GeV);
auto const fullSequence = switch << energyLoss << ...