Add package versioning scheme

[josephmckinsey]

We could extend the component_definition.json or create a new .json with :

1. Version numbers and corresponding git-tags or revisions
2. Package location (git repository and subdirectory)
3. Dependencies and compatibility version ranges for all version numbers

We would use the list of version numbers and version ranges to construct a working example via a dependency resolution algorithm. Semantic versioning would allow us to indicate breaking changes, and individual component authors would have the choice of whether to update to newer component versions or not.