Replay option for primaries instead of Recreate

[Laurie Nevay]

We have --recreate to rerun a previous BDSIM run from an output file. This sets the options exactly and forces the seed to be reloaded from the output file at the start of each event. With the same software and inputs this allows us to recreate a simulation exactly, and potentially jump N events into that run and recreate just that 1 event.

However, it would be useful to ‘replay’ a simulation but allow the seeds to be free. In effect, only replaying the primaries from the output file and ignoring all other options settings.

I have just added using a sampler from an output file as the primary distribution in another simulation, so this is very similar, but that we would ignore beam parameters in the input (except the design particle species and E,Ek,P).

[Laurie Nevay]

Better rephrased as allowing the bdsimsampler distribution to read the Primary branch.