Add versioning to templates

[SamJakob]

As a blocker to #2, we need a way to version templates (and we should probably get out ahead on specifying which template was used, in case we go as far as adding multiple templates in future).

• Decide on a method of storing the version system and template name.
• Document in this ticket how we can check for updates with version number (if custom infrastructure needed, so be it).
• Add the versioning mechanism to create-cinnamon-project.