Improvement: Get rid of coffeescript dependency

[woidda]

Actually this is a pretty easy task. If I had more time to be able to do the intial setup -- checking out rep etc -- I would do this via a pull request.

CoffeeScript is kind of obsolete with modern versions of ES and TypeScript.

Hence, this just as a small improvement suggestion:

• There are only a couple of CoffeeScript files in this repo
• With decaffeinate these transfiles are translated to ES6 in seconds (it works pretty well -- I tried it with the files)
• Then you can remove the coffee-rails dependency.

Thanks to anybody willing to do this. This makes a lot of projects using this gem leaner.

[mshibuya]

It would be fantastic, waiting for PR!

[RocKhalil]

Will try to do it myself this week :-)

[mroderick]

@mshibuya #3168 removes CoffeeScript from this project

[GMorisot]

To note... If you add CKeditor to Rails admin, the bit of code in the docs to make it work in nested forms depends on coffeescript.