Added example plugin registry

Change-Id: I80daa31b6bdbaa9e6d6e81d62e6c34400509844a
diff --git a/dev/demo/plugin-server.html b/dev/demo/plugin-server.html
index 0d4a454..d91b9e2 100644
--- a/dev/demo/plugin-server.html
+++ b/dev/demo/plugin-server.html
@@ -16,7 +16,7 @@
         <ol>
           <li class="active">
             <div id="container"></div>
-            <a onclick="KorAP.Plugin.addWidget(document.getElementById('container'), 'Example', 'http://localhost:3003/demo/plugin-client.html')">Open widget</a>
+            <div id="buttons"></div>
           </li>
         </ol>
       </div>