Add node reference support

Currently, node reference fields aren't made available in the translation editor, because CCK support is tied to $node->field[0]['value'] rather than $node->field[0]['nid'].

This patch add support for node reference fields to pass through the translation workflow. The focus is on setting the translated version of the referenced node in the target language automatically. So, node reference fields use the text input field in the form "Node title [nid: NID]" (and assumes this pattern doesn't occur in other fields) (there isn't an existing method in the architecture to distinguish different types of CCK fields to easily tap into). The node reference fields are collapsed, disabled for editing and automatically checked as "finished" in the translation editor.