Investigate elegant solution for variables VER_1_LATEST & VER_XML_LATEST

During the Review Phase of OpenSCENARIO there occured some problems with version variables. We did a quick fix for the release of OpenSCENARIO DSL 2.1.0 but this should be investigated and a more elegant solution should be found for the future.

Shall be handled after the release of OpenSCENARIO DSL 2.1.0