Add visual indicator for unused packages

[smeijer]

The one thing that this package is missing, that would make it truly awesome (IMO).

A visual indicator if the package seems to be unused. It doesn't need to be a guarantee. I think a quick scan for imports or requires would be sufficient.

The further analyses could be done manually.

About visual indicators. "dependency" / "devDependency" hinting would be useful as well. Babel and Eslint plugins, are usually defined as dev-dependency. A hint like: "shouldn't this be a dev-dependency?", (or the opposite) would be very useful for starting developers.