Add admin link to tools dropdown menu

At the moment the only way to get to the index is to manually type in
the URL, which is a little inconvenent. Add a link to the Tools
drop-down (visible only for users with admin access) that will take you
to it for convenience.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

templates/base.html

@@ -84,6 +84,9 @@
                             {% if rrs_enabled %}
                             <li><a href="{% url 'rrs_frontpage' %}">Recipe Maintenance</a></li>
                             {% endif %}
+                            {% if user.is_staff %}
+                            <li><a href="{% url 'admin:index' %}">Admin</a></li>
+                            {% endif %}
                         </ul>
                     </li>
                     {% endif %}