more effective subsets

• cache subsets for node group moving
• add settings:
  • maxDepth (default: false) false or a numeral. If set to a numeral, limits the level of depth that the the diff mechanism looks for differences. If false, goes through the entire tree.
  • maxChildCount (default: 50) false or a numeral. If set to a numeral, does not try to diff the contents of nodes with more children if there are more than maxChildDiffCount differences among child nodes.