Add color parameter to custom the datepicker design

[RemiAWE]

It will be great to have the possibility to custom the display of the Datepicker without having to rewrite the whole SASS or CSS file. It would be a better integration in every projects.

Update: After a little brainstorming, it would be better to not have any color variable in the js scripts. The best solution is to have a base structure CSS file and a theme CSS file. So there would be no code to add to the Datepicker and it would stay lightweight and 100% logic without style in JS.