Various accessibility improvements

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

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

js/src/views/Discussions/Create.vue

@@ -55,7 +55,7 @@
       </b-field>
 
       <b-field :label="$t('Text')">
-        <editor v-model="discussion.text" />
+        <editor v-model="discussion.text" :aria-label="$t('Comment body')" />
       </b-field>
 
       <button class="button is-primary" type="submit">

js/src/views/Discussions/Discussion.vue

@@ -125,7 +125,7 @@
       >
       <form @submit.prevent="reply" v-if="!error">
         <b-field :label="$t('Text')">
-          <editor v-model="newComment" />
+          <editor v-model="newComment" :aria-label="$t('Comment body')" />
         </b-field>
         <b-button
           native-type="submit"