Control Templates need Versioning

With the introduction of multiple templates for the same control we will require template versioning to ensure backwards compatibility with old template projects.

Actions points:

• Version the QML template code. Add "//TV: xx" on top of the QML template code.
• Attach the new template code
• AssetImporter should read the version tag and avoid code paths according to the version
• Add an info message in the import dialog about the template version used.