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.
<xsd:attribute name="Compiler" type="xsd:string" use="optional" default="gcc"/>
<xsd:attribute name="CFLAGS" type="xsd:string" use="optional" default=""/>
<xsd:attribute name="Linker" type="xsd:string" use="optional" default="gcc"/>
<xsd:attribute name="LDFLAGS" type="xsd:string" use="optional" default=""/>