Make WebPack generate two JS bundles

[maxpatiiuk]

Currently, WebPack outputs JS code with a lot of polyfills to support old and non-spec-compliant browsers.
Instead, WebPack should be made two output two bundles: one would be served for customers with modern browsers, and the other for old browsers.
This will provide better experience for users of modern browsers.

Additionally, it would be worth considering disabling all those polyfils in development to speed up build process