Add generation of XML files for use in tests
For a textual comparison of XMl files, it is necessary that the output is reproducible (sorted), which is made possible with this implementation, but not with QDomDocument, QXml...Writer.
For a textual comparison of XMl files, it is necessary that the output is reproducible (sorted), which is made possible with this implementation, but not with QDomDocument, QXml...Writer.