[WIP] bootstrap-chosen for Bootstrap 4

[PascaleBeier]

Hey folks,

First of all, thanks so much @alxlit for making our lifes a little easier the last 5 years. I'm so grateful for your time and effort put into this project.

With no sign of activity or revival, I forked this project to bootstrap4-chosen with the main goal of, well, Bootstrap 4 compat.

While most of the fork is working already (mostly switching out mixins and variables), there still needs to be some tuning, as you can see in the examples.

Any help and feedback is surely appreciated!

Have a nice day!