Move Packet 'properties' from core to extensions

Code for Jive's packet properties should not be in 'core'. Also
de-serializing input from network causes some security implications, it
is therefore disabled as default.

documentation/extensions/intro.html

@@ -90,6 +90,11 @@
             <td><a href="http://www.xmpp.org/extensions/xep-0332.html">XEP-0332</a></td>
             <td>Allows to transport HTTP communication over XMPP peer-to-peer networks.</td>
         </tr>
+        <tr>
+            <td><a href="properties.html">Jive Properties</a></td>
+            <td>N/A</td>
+            <td>TODO</td>
+        </tr>
     </table>
 </body>
 </html>