Various accessibility improvements

* Add announcement element with `aria-live`
* Add skip to main content element

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/package.json

@@ -29,6 +29,8 @@
     "@tiptap/extension-underline": "^2.0.0-beta.7",
     "@tiptap/starter-kit": "^2.0.0-beta.37",
     "@tiptap/vue-2": "^2.0.0-beta.21",
+    "@vue-a11y/announcer": "^2.1.0",
+    "@vue-a11y/skip-to": "^2.1.2",
     "@vue/apollo-option": "4.0.0-alpha.11",
     "apollo-absinthe-upload-link": "^1.5.0",
     "blurhash": "^1.1.3",