@Override
    public void start() throws IllegalStateException {
        super.start();
        infoHandler.setServerNodeInfoProvider(NAMESPACE, this);
        itemsHandler.setServerNodeInfoProvider(NAMESPACE, this);
    }
Implements JEP-0013: Flexible Offline Message Retrieval. Allows users to request number of
messages, request message headers, retrieve specific messages, remove specific messages,
retrieve all messages and remove all messages.

@author Gaston Dombiak
xmppserver/src/main/java/org/jivesoftware/openfire/handler/IQOfflineMessagesHandler.java