Additional widget to include as standard

[Triloworld]

Hello,
I find that module isn't incorporate "netlify-identity-widget.js (https://github.com/netlify/netlify-identity-widget)" as standard.
Right now, only by downloading it and adding to "netlify-cms" will work (tips for other looking for solution).

Good think will be to add as package and use settings to add/remove it from bundle.
There is plenty of issues to resolve. My is about new feature but good in term of usability.