Feature: Reseed a running experiment

[Qwlouse]

It would be useful be able to restart the seeding at any point even while running an experiment.

[Qwlouse]

Actually after thinking about this, I am not sure anymore that this is actually a good idea. Once a run has started we want it to finish without any interaction. This way we can keep it reproducible.

The only usecase that I can think of is if you want to systematically rerun some of your functions with the same seed multiple times. But this can already be achived by explicitly passing the _seed resp. the _rnd argument. The only problem with that is, that the determinism won't propagate to function calls within that function. But that would be extremely tricky to implement.

We could allow to reseed individual Ingredients, but that would also have to be handled with care.