Use "files" whitelist instead of .npmignore

[PTaylour]

why?

In the eyes of npm .npmignore replaces .gitignore.

This is hard to maintain as the gitignore is pretty much always a subset of the npmignore

Also, we'd rather whitelist than blacklist. There are many more things to exclude than include.

The package.json files field lets us to this.

see https://blog.npmjs.org/post/165769683050/publishing-what-you-mean-to-publish

[PTaylour]

@reecelucas is this inline with your update to production-ui-core?

[reecelucas]

@PTaylour, I also added README.md but I don't think it's essential.

[PTaylour]

Yea appaz these are always included

package.json README CHANGES / CHANGELOG / HISTORY LICENSE / LICENCE NOTICE The file in the "main" field

[PTaylour]

PR 100 merged 🍾