Merge branch 'feature/ISTWCMS-5595-m26lebla-site-container' into '1.0.x'

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

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

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

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

src/patterns/03-layouts/_index.scss

src/patterns/03-layouts/content/_content.scss

src/patterns/03-layouts/content/content.md

src/patterns/03-layouts/content/content.twig

src/patterns/03-layouts/footer/_footer.scss

src/patterns/03-layouts/footer/footer.md

src/patterns/03-layouts/footer/footer.twig

src/patterns/03-layouts/footer/footer.yml

src/patterns/03-layouts/header/_header.scss

src/patterns/03-layouts/header/header.md

src/patterns/03-layouts/header/header.twig

src/patterns/03-layouts/header/header.yml

src/patterns/03-layouts/layout/_layout-base.scss

...tterns/03-layouts/layout/layout--1-col/layout--1-col.twig

...tterns/03-layouts/layout/layout--2-col/layout--2-col.twig

...tterns/03-layouts/layout/layout--3-col/layout--3-col.twig