code: function downloadFromClick(page, ph, selector, callback) {
      const HREF_KEY = 'href';
      async.waterfall([
          function (callback) {
              getSelectorAttribute(page, ph, [selector, HREF_KEY], callback);
          },
          function (page, ph, relativeHref, callback) {
              getCurrentUrl(page, ph, function (error, page, ph, currentUrl) {
                  if (error) {
                      callback(error, page, ph);
                      return;
                  }
                  callback(null, page, ph, currentUrl + relativeHref);
              });
          },
          function (page, ph, url, callback) {
              downloadFromUrl(page, ph, url, callback);
          }
      ], callback);
  }
docs: Clicks an element on the page and downloads the file behind the element
  @param page
  @param ph
  @param {string} selector
  @param {pageResultCallback} callback