tweak-pr-148-per-suggestions

[RichardBruskiewich]

Iterated on PR 148 tweaks suggested by Sierra, plus related enhancements (and unit tests): Moved method-internal defined match_associations() function into Toolkit level method (with docs); allow 'match all' of subject, predicate, object slots with descriptions, and to predicates when no predicate slot is seen in slot_usage of a given association; add shallow (one level) is_a hierarchy traversal for slot_usage property discovery; removed some unused imports; remove spurious 'if not association' check code in get_associations() method; all unit tests pass

[sonarcloud[bot]]

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