[enh] show js warning only if menu can't be used or inside preferences

searx/templates/oscar/base.html

     {% endblock %}
     {% block site_alert_warning_nojs %}
     <noscript>
+        <div class="visible-xs-block">
         {% include 'oscar/messages/js_disabled.html' %}
+        </div>
     </noscript>
     {% endblock %}
     {% block site_alert_info %}

searx/templates/oscar/preferences.html

 {% extends "oscar/base.html" %}
 {% block title %}{{ _('preferences') }} - {% endblock %}
+{% block site_alert_warning_nojs %}
+<noscript>
+    {% include 'oscar/messages/js_disabled.html' %}
+</noscript>
+{% endblock %}
 {% block content %}
 <div>