better support for extension object from xml, split binary code

If node value is type Guid get the value from the child <string> tag.

fixes for opcua-modeler

* ignore BadNoSubscription after deleting the last subscriptions

Spec Part 5, Paragraph 13.8.1 says that outstanding publish responses
should be answered with BadNoSubscription in case the client just
deleted the last subscription.

This can lead to the following exchange:

-> Publish
-> Delete
<- Publish response (BadNoSubscription)
-> Delete response

We did not correctly ignore BadNoSubscription in this case.

* check response of close session request

initial copy_node implementation and cleanup of instanciate