Replace jQuery.extend with Object.assign

[OleVik]

Support is virtually full for all browsers (ref), if needed a polyfill could be thrown in. Results should be equal with jQuery (test). Fixes #290.

[w00fz]

I’m ok with the change but would definitely prefer to see the polyfill in place. I’ve seen issues still with IE Edge and with this being also frontend plugin it’s probably best to be safer than sorry.
I also think this is not the only place where we do extend in the plugin, was it?

[OleVik]

The only other place jQuery.extend is used is in the file-field, which requires jQuery outright. Could potentially be replaced with vanilla JS too, but this PR only backfills in where jQuery isn't really needed. I'll look at adding in the polyfill, which should resolve some IE issues if I'm not mistaken.

[OleVik]

Latest commit adds the polyfill, though as noted it needs to be compiled. The webpack and gulp setups won't run on my Windows DevEnv, but with the polyfill included (but not jQuery), it throws no errors in MS Edge.

[drzraf]

See #305
But even then, I have:
Error: webpack.optimize.UglifyJsPlugin has been removed, please use config.optimization.minimize instead.

But running webpack directly works:
NODE_ENV=production ./node_modules/.bin/webpack --config webpack.conf.js --mode production

[w00fz]

This looks good now @OleVik but where are you loading the polyfill from?

[w00fz]

@OleVik Actually I missed your message, I'll look at adding it in the mix and transpiling.

Cheers

[w00fz]

@OleVik @drzraf I am now loading the polyfill for IE only, can you guys give this a try? 10bd598