Change adding query parameters

[rlabrovi]

I'm unable to manupilate batch action button because you are forcing ? when appending query params to button href.

Please change:

  buttons.forEach(function(button){
      button.addEventListener('click', function(event){
        button.href += '?' + selectedItemIds()
      });
    });

to

     buttons.forEach(function(button){
                button.addEventListener('click', function(event){
                    if (button.href.includes('?')) {
                        button.href += '&' + selectedItemIds();
                    } else {
                        button.href += '?' + selectedItemIds();
                    }
                });
            });

[andreibondarev]

@rlabrovi Would you please open a PR if you get a chance? Also -- can we use a cleaner way of constructing an href URL with params, maybe wrapping the params into URLSearchParams?