[enh] rendering engine names

searx/templates/index.html

     <form method="post" action="">
         <input type="text" name="q" tabindex="1" />
         <input type="submit" value="search" />
+        <p>
+        {% for engine in engines %}
+            {{ engine }}: <input type="checkbox" name="engine_{{ engine }}" checked="checked"/>
+        {% endfor %}
+        </p>
     </form>
 </div>
 {% endblock %}