Add support to find and concatenate selector

Thanks for this contribution @robpowell. I really like the way that you added extra params to make it more versatile.

I was concerned about having a finder that is called differently than the plucker, so expanded existing plucker to user your logic and then made the finder just call the plucker with the pluck flag set to false.

I also added another arg that lets you control the separator.

/**
   * Finder crawls $selector elements and concats them as it goes.
   *
   * @param string $selector
   *   The selector to find.
   * @param string $method
   *   (optional) The method to use on the element, text or html. Default: text.
   * @param string $qp_method
   *   (optional) The QueryPath method to use.
   * @param string $separator
   *   (optional)  The separator to use between the concatenation.
   *
   * @return string
   *   Concatenation of all selector elements' text.
   */
  protected function findAndConcatAnySelector