Reshape Idavoll as a PubSubResource. PubSubResource is Wokkel's newer interface for building (parts of) XMPP publish-subscribe services and replaces the old interface of PubSubService. It is more flexible for adding new protocol, allows for node-as-code (providing a specific backend per node), and permits accepting requests for different entities (virtual hosts or PEP-like settings). This moves over the current backend to use the new interface, so new code for previously unsupported protocol can be added down the line.