Lightbox factorisation partial (#596)

assets/sass/_theme/blocks/gallery.sass

assets/sass/_theme/components/lightbox.sass

assets/sass/_theme/hugo-osuny.sass

assets/sass/_theme/utils/shame.sass

layouts/partials/blocks/templates/chapter.html

layouts/partials/blocks/templates/gallery.html

...uts/partials/blocks/templates/gallery/carousel-image.html

layouts/partials/blocks/templates/gallery/grid.html

layouts/partials/blocks/templates/gallery/images.html

layouts/partials/blocks/templates/gallery/large.html

layouts/partials/blocks/templates/image.html

layouts/partials/commons/image-figure.html

layouts/partials/commons/lightbox/lightbox-launcher.html

layouts/partials/header/hero.html