new SingletoneTaxonomy and SingletoneInstanceTaxonomy to represent
inconsistent taxonomies; modified tests accordingly, moved
MockInstanceTaxonomy to tests; improved documentation
Merge branch 'master' into feature/incremental-taxonomy
ConcurrentInstanceTaxonomy: removeNode was not thread safe;
RandomWalkIncrementalRealizationCorrectnessTest failed for
testBasicABox; fixed
TaxonomyCleaning: submitClass was not correct and thread safe
(RandomWalkIncrementalRealizationCorrectnessTest testInconsistent gets
npE when the same node is processed by two workers). Fixed by now, but
the code is still shaky.