Make normalization methods for `AsynchronousPerturbationGraph` public

[daemontus]

Currently, AsynchronousPerturbationGraph uses two Boolean networks that are created from the original network through normalization and syntactic manipulation. They can be accessed using the getter methods on the graph itself, but there is no way to create them without creating the graph.

We might want to add these methods to the static API of the perturbation graph, so that anyone can create a network extended with perturbation parameters if they so desire. However, it should be noted that due to differences in regulations, the unit set of the new network might not be the same as the normalized networks (we currently solve it by providing a custom unit set).