Merge changes I9886ddb7,I851fa16e,I3b7b0bf5,Ib7f2ce87,I7d0cf295,I35ae6fcb,I14c86257...

* changes:
  LazyNodeToNodeMap: use a ArrayDeque instead of a Stack
  XmlTreeBuilder: ensure thread safety
  NodeFactory: use an ArrayDeque instead of a Stack
  NodeUtils: Use an ArrayDeque instead of a Stack
  Optimize YangParserListenerImpl logging
  BUG-865: migrate to Optional<>
  Refactor SchemaPathStack
  Migrate the conceptual stack into a utility class