Permit setting seed for multiple stochastic ensemble simulations

[TorkelE]

When performing ensemble simulations of a stochastic problem, and you set a seed argument, that seed is automatically sent to each single simulation, resulting in identical results for each.

It would be useful to have a usable way to set seed for ensemble simulations. Even if we don't want a single seed to affect each simulation independently, permitting a vector of seeds might make sense.

[ChrisRackauckas]

I'm not sure how it would be done. solve keyword arguments are always ensemble-global, so to keep to it seed would be ensemble global. But you can always put keyword arguments on the prob in an ensemble if you want it to be prob-specific, so that would be what I would recommend. We could specialize the seed argument in ensembles, but we'd want to make that a system and not just some (undocumented) one-off different piece.