Avoid trying to satisfy requirements in any order

The order in which requirements are satisfied has no effect on the time slots which are chosen for sampling, but it can influence the aggregate sample counts as even equivalent samples are count equally for the target function. We can however still avoid enumerating all different orders by always fulfilling that requirement which needs the smallest number of samples first. Since the number of requirements determines the number of their orderings via the factorial function, this significantly reduces the search space and for example let's the R script finish in the full 27 requirement problem in under 30s.