Solve import order problem when POULibrary imports ConfigTreeNode because of UserAddressedException. Now UserAddressedException is declared in POULibrary.py, as a quick and dirty fix, but some independant module should be created for beremiz exceptions in general.

<?xml version='1.0' encoding='utf-8'?>
<BeremizRoot xmlns:xsd="http://www.w3.org/2001/XMLSchema" URI_location="LOCAL://">
  <TargetType/>
  <Libraries Enable_Python_Library="false"/>
</BeremizRoot>