Add link to admin page

- Only if user is admin!

InvenTree/templates/navbar.html

@@ -16,6 +16,9 @@
       <li class='dropdown'>
           <a class='dropdown-toggle' data-toggle='dropdown' href="#"><span class="glyphicon glyphicon-user"></span>{{ user.get_username }}</a>
           <ul class='dropdown-menu'>
+              {% if user.is_staff %}
+              <li><a href="/admin/">Admin</a></li>
+              {% endif %}
               <li><a href="{% url 'logout' %}">Logout</a></li>
           </ul>
       </li>