[enh] implements #264 : add rel="noreferrer" to external links

searx/templates/default/infobox.html

@@ -17,7 +17,7 @@
     <div class="urls">
         <ul>
             {% for url in infobox.urls %}
-            <li class="url"><a href="{{ url.url }}">{{ url.title }}</a></li>
+            <li class="url"><a href="{{ url.url }}" rel="noreferrer">{{ url.title }}</a></li>
             {% endfor %}
         </ul>
     </div>