Generate `QNProblemSet`s without the `StateTransitionManager`

[grayson-helmholz]

Continuing the recreation of the functionality of the StateTransitionManager of Issue #272 , the generation of the QNProblemSets could also be done without it.

[redeboer]

Yes good idea, this is also related to #20.

Perhaps it's best to start writing out the steps that are required to generate QNProblemSets, for instance, by summarizing how the STM does it. We could then think of an interface or set of functions that can do this separately.