NonRedundantRuleApplicationConclusionVisitor implemented directly using
Conclusion interfaces; refined some generic parameters in visitors using
the ? super C wildcard.
finished moving rule application methods to visitors over conclusions.
Visitors can now be composed with "null" visitors, which are ignored
(useful for switching off some visitors). Using this strategy for
counting processed / used conclusions.
HybridLocalRuleApplicationConclusionVisitor slightly simplified
some simplification for conclusion visitors; printing produced
conclusion counts