SVGHMI: Makes error when HMI tree is not well formed. Prevents multiple and non-first HMI_NODE, and ensure that all paths in HMI tree are unique.

<?xml version='1.0' encoding='utf-8'?>
<BaseParams xmlns:xsd="http://www.w3.org/2001/XMLSchema" IEC_Channel="0" Name="ModbusTCPclient_0"/>