OPC-UA: Update CTN "ChangesToSave" status when variable selection change.
- fixes changes not being saved when no other changes happening to configuration
- added CTNMarkModified to ConfigTreeNode in order to generalize
<xsd:element name="Xenomai">
<xsd:complexType>
%(toolchain_gcc)s
<xsd:attribute name="XenoConfig" type="xsd:string" use="optional" default="xeno-config"/>
</xsd:complexType>
</xsd:element>