Fix RGAA v4 criterias 9.1 and 9.2 on page structure (nav and h1)

src/app/core/components/feedback/feedback.component.html

...p/core/components/main/side-menu/side-menu.component.html

src/app/datasets/components/results/results.component.html

src/app/editorialisation/components/home/home.component.html

src/app/editorialisation/components/home/home.component.scss

.../shared/components/page-header/page-header.component.html

.../shared/components/page-header/page-header.component.scss

src/i18n/messages.en.xlf

src/i18n/messages.fr.xlf