[A11Y] Ajout d'attributs aria (#592)

layouts/partials/blocks/templates/call_to_action.html

layouts/partials/blocks/templates/chapter.html

layouts/partials/blocks/templates/features.html

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

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

layouts/partials/blocks/templates/image.html

layouts/partials/blocks/templates/testimonials/single.html

layouts/partials/footer/footer.html

layouts/partials/header/header.html

layouts/partials/programs/image.html