Investigate expected functionality of dependencies

[eAlasdair]

Every interactive that uses a third-party library has its own package.json file listing the versions of each dependency it requires. However, I have noticed that all interactives that use a library will use the same version of it – even if the jsons specify different versions. If the dependency is defined elsewhere an interactive doesn't even need its own package.json (except to be self-contained). Plus they don't necessarily use the latest version of all the ones defined.

We should investigate if this is expected functionality, as well as the potential effects this could have on future interactives needing newer versions of existing dependencies.