Add FatalError() method to ConfigTreeNode.
Extensions can report error addressed to user, without a traceback.
<?xml version='1.0' encoding='utf-8'?>
<BeremizRoot xmlns:xsd="http://www.w3.org/2001/XMLSchema" URI_location="LOCAL://">
<TargetType>
<Linux/>
</TargetType>
</BeremizRoot>