Design template versioning story.

[guptasu]

We need to allow template developers to make breaking changes to their template via some versioning mechanism.

[guptasu]

@geeknoid @mandarjog @douglas-reid FYI. I think we need to think about this during this quarter.. Versioning scares me, since beta is our last shot for us to enable ourselves + the template developers to make breaking changes in the future.