referer: do not send referrer when opening a link

This change augments what was already done in 54e0f2de5b (PR with discussion
at #3636).

For documentation about the meaning of "noopener, noreferrer", see:
https://developer.mozilla.org/en-US/docs/Web/API/Window/open#Window_functionality_features

src/static/js/ace2_inner.js

@@ -3374,8 +3374,7 @@ function Ace2Inner(){
       {
         try
         {
-          var newWindow = window.open(n.href, '_blank');
-          newWindow.focus();
+          window.open(n.href, '_blank', 'noopener,noreferrer');
         }
         catch (e)
         {