fix: Proxy logic in trame

[jafranc]

Few fixes on trame to avoid crashes. The following behavior was not working:

• Change data in a A-node in the tree, select another B-node of the tree (so A-node changes are commited to the proxy) and then go back to to A-node toggling editor, the change should be visible in XML.
• Output to XML was crashing if edited (33f186d)
• Changes where not reflected in the new XML