attachments: provide correct context for alt/title attributes instead of the previous hack

src/components/attachment/attachment.vue

@@ -25,9 +25,9 @@
       class="image-attachment"
       :class="{'hidden': hidden && preloadImage }"
       :href="attachment.url" target="_blank"
-      :title="attachment.description"
     >
-      <StillImage :referrerpolicy="referrerpolicy" :mimetype="attachment.mimetype" :src="attachment.large_thumb_url || attachment.url"/>
+      <StillImage :referrerpolicy="referrerpolicy" :mimetype="attachment.mimetype" :src="attachment.large_thumb_url || attachment.url"
+       :alt="attachment.description"/>
     </a>
 
     <a class="video-container"

src/components/still-image/still-image.js

@@ -3,7 +3,8 @@ const StillImage = {
     'src',
     'referrerpolicy',
     'mimetype',
-    'imageLoadError'
+    'imageLoadError',
+    'alt'
   ],
   data () {
     return {

src/components/still-image/still-image.vue

@@ -1,7 +1,7 @@
 <template>
   <div class='still-image' :class='{ animated: animated }'>
     <canvas ref="canvas" v-if="animated"></canvas>
-    <img ref="src" :src="src" :referrerpolicy="referrerpolicy" v-on:load="onLoad" @error="onError"/>
+    <img ref="src" :alt="alt" :title="alt" :src="src" :referrerpolicy="referrerpolicy" v-on:load="onLoad" @error="onError"/>
   </div>
 </template>