Enable eslint-plugin-imports

Via @rye 

> Can we organize these a little more nicely?
> 
> I like:
> 
> - Imports from all externals up top
> - Imports from our own modules after those
> - Imports from everywhere else after that (in this case, lib/storage)?

[`eslint-plugin-import`](https://github.com/import-js/eslint-plugin-import) can do that! We should set it up.