Add version tag to saved transformation rules

[csnyulas]

When saving transformation rules to file, we should add a version tag that would identify the version of the Mapping Master DSL that was used for these rules. To simplify the management of these tags, we could refer to the version of the MM library itself. If a user loads a rules file which was created with an older version (not having a tag we assume it was created with MM v.1.0.0), we could point them to a wiki page where they can find an overview of all the changes that took place between the different versions, which would allow the user to quickly and easily update their rules to the new version of the language.