Get node by path

This is really for unit testing convenience and enables the following

  $node = $qn->getNodeByPath('where.constraint.operand_dynamic[1]);
  $node = $qn->getNodeByPath('order_by.ordering[2].operand_dynamic);
Created TestQueryBuilder
Added getPath and dumpPaths
Merge pull request #331 from dantleech/qb_get_node_by_path_1

Get node by path