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.