SVGHMI: Simplification and optimization. func:parselabel becomes a template.

All labels are parsed into a global variable containing resulting widget
description as a node-set. func:widget(id) was added for random access to
widget description.

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<?xml version='1.0' encoding='utf-8'?>

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<BaseParams xmlns:xsd="http://www.w3.org/2001/XMLSchema" IEC_Channel="0" Name="svghmi_0"/>