auth: Split UI pages into admin and non-admin ones.

appengine/components/components/auth/ui/templates/admin/access_denied.html

-{% extends 'auth/base_minimal.html' %}
+{% extends 'auth/admin/base.html' %}
 {% block content %}
 
 <h2>Access denied</h2>
 <p>Looks like you do not have access to this page. You are logged in as
 <b>{{identity.name}}</b>.
 <p>Login under a different account.</p>
 <hr>
 <p>Error details:</p>
 <pre>{{error}}</pre>
 <hr>
 <p>
   <a id="logout-btn" class="btn btn-primary" href="#">Logout</a>
 </p>
 
 <script type="text/javascript" nonce="{{csp_nonce}}">
   $('#logout-btn').click(function(e) {
-    common.logout();
+    redirectToLogout();
     e.preventDefault();
   });
 </script>
 
 {% endblock %}