Actually fix the Referrer issue

Before this patch I managed to send a bunch of referrers to third party websites with Firefox. Unfortunately, meta name="referrer" isn't enough.
I added "noopener" because that's also what Nextcloud does. One may want to check another pull request from 2015 which may be more complete, but it was denied with a plugin proposal: ether#2498
References to earlier issues: ether#1603, ether#3043

src/static/js/domline.js

@@ -198,7 +198,7 @@ domline.createDomLine = function(nonEmpty, doesWrap, optBrowser, optDocument)
         {
           href = "http://"+href;
         }
-        extraOpenTags = extraOpenTags + '<a href="' + Security.escapeHTMLAttribute(href) + '">';
+        extraOpenTags = extraOpenTags + '<a href="' + Security.escapeHTMLAttribute(href) + '" rel="noreferrer noopener">';
         extraCloseTags = '</a>' + extraCloseTags;
       }
       if (simpleTags)