add basic deletes support that works with masto WS

src/components/user_avatar/user_avatar.vue

@@ -1,5 +1,6 @@
 <template>
   <StillImage
+    v-if="user"
     class="Avatar"
     :alt="user.screen_name"
     :title="user.screen_name"
@@ -7,6 +8,11 @@
     :class="{ 'avatar-compact': compact, 'better-shadow': betterShadow }"
     :image-load-error="imageLoadError"
   />
+  <div
+    v-else
+    class="Avatar -placeholder"
+    :class="{ 'avatar-compact': compact }"
+  />
 </template>
 
 <script src="./user_avatar.js"></script>
@@ -42,5 +48,10 @@
     border-radius: $fallback--avatarAltRadius;
     border-radius: var(--avatarAltRadius, $fallback--avatarAltRadius);
   }
+
+  &.-placeholder {
+    background-color: $fallback--fg;
+    background-color: var(--fg, $fallback--fg);
+  }
 }
 </style>