introducing TaxonomyState to hold the taxonomy and other information,
e.g., for which classes the nodes have been modified/cleaned
clean-up
using the random seed provider, as in other randomized tests
class taxonomy now updated w/o an iteration over all indexed atomic
classes; instead, the taxonomy state keeps a set of all classes whose
taxonomy nodes have been modified.
re-created the list of all added classes in the differential index, now
used for taxonomy updates