ISTWCMS-5596: addition of the button element, component, mixin

src/patterns/01-core/elements/_details.scss

src/patterns/01-core/mixins/_button.scss

src/patterns/01-core/mixins/_index.scss

src/patterns/01-core/props/_colors.scss

src/patterns/04-components/_index.scss

src/patterns/04-components/button/_button.scss

...rns/04-components/button/button--cancel/button--cancel.md

...s/04-components/button/button--cancel/button--cancel.twig

...ns/04-components/button/button--cancel/button--cancel.yml

...rns/04-components/button/button--danger/button--danger.md

...s/04-components/button/button--danger/button--danger.twig

...ns/04-components/button/button--danger/button--danger.yml

...terns/04-components/button/button--large/button--large.md

...rns/04-components/button/button--large/button--large.twig

...erns/04-components/button/button--large/button--large.yml

...rns/04-components/button/button--medium/button--medium.md

...s/04-components/button/button--medium/button--medium.twig

...ns/04-components/button/button--medium/button--medium.yml

...s/04-components/button/button--primary/button--primary.md

...04-components/button/button--primary/button--primary.twig