SVGHMI: widgets are not anymore binary relative or absolute, but have a "relativeness".

Because of allowing multiple variables per widget, we must distinguish if individual variables is relative to page, not the whole widget.

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                  <xsd:element name="Linux">

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                    <xsd:complexType>

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                      %(toolchain_gcc)s

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                    </xsd:complexType>

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                  </xsd:element>