SVGHMI: Prepare accepting multiple clients on multiple HMI: Use POULibrary new capability to add variables to PLC Configuration. Now heartbeat and HMI tree root are added by the library part of SVGHMI, and not by each instance.

<?xml version='1.0' encoding='utf-8'?>
<BeremizRoot xmlns:xsd="http://www.w3.org/2001/XMLSchema" URI_location="WAMP://127.0.0.1:8888#Automation#wamptest">
  <TargetType/>
</BeremizRoot>