Un-minified bundled js

**Is your feature request related to a problem? Please describe.**

Often I find myself looking at call stacks like this:


And it's usually because I've done something stupid, but netlify-cms is not being very helpful in my attempt to figure out _what_ I did.

**Describe the solution you'd like**

Two `.js` outputs in the dist folder of the `netlify-cms` package (ideally, also the various other packages like `netlify-cms-app` etc. but `netlify-cms` would be a good start). Similar to [js-yaml](https://unpkg.com/browse/js-yaml@3.12.0/dist/):


Then the docs could be updated to refer to `index.min.js` instead of `index.js`. Or, to avoid accidentally expanding bundle sizes, they could be named `index.js` and `index.unminified.js`.