insertOrderedList: implement listifying

Apart from tests of issue #39, this CL passes all listifying tests.

PTAL
How about using |every|?

var stopped = [].every.call(nextSiblingNode.childNodes, (node) => {
  if (lists.indexOf(node) === -1)
    return false;
  listToBeMerged.push(node);
  return true;
});