4.0.0.alpha - Drop of Jquery

Enforce checbox default background color

otherwise, in case validation fails on a checkbox, https://github.com/cprodhomme/arctic_admin/blob/76af378f4fda01783a838d9ea157ce82a6bc6b3b/app/assets/stylesheets/arctic_admin/components/_form.scss#L29..L33 overwrites it and checking only works internally but no visual change can be seen