Authorize access to admin panel, etc.

Adds a separate admin namespace and base controller, with authorization
by looking up the admin property in the user's LDAP account.

app/views/admin/ldap_users/index.html.erb

@@ -0,0 +1,27 @@
+<h2>LDAP users</h2>
+
+<ul>
+  <li><%= link_to 'kosmos.org', admin_ldap_users_path %></li>
+  <li><%= link_to '5apps.com', admin_ldap_users_path(ou: '5apps.com') %></li>
+</ul>
+
+<table>
+  <thead>
+    <tr>
+      <th>UID</th>
+      <th>E-Mail</th>
+      <th>Admin</th>
+      <!-- <th>Password</th> -->
+    </tr>
+  </thead>
+  <tbody>
+    <% @entries.each do |entry| %>
+    <tr>
+      <td><%= entry[:uid] %></td>
+      <td><%= entry[:mail] %></td>
+      <td><%= entry[:admin] %></td>
+      <!-- <td><%= entry[:password] %></td> -->
+    </tr>
+    <% end %>
+  </tbody>
+</table>