Implement "seen by" functionality

src/components/messages/MessageOutgoing.vue

@@ -25,14 +25,17 @@
       <span v-else class="white--text headline">{{ userAvatarLetter }}</span>
     </v-avatar>
     <QuickReactions :event="event" :timelineSet="timelineSet" v-on="$listeners"/>
+    <SeenBy :room="room" :event="event"/>
   </div>
 </template>
 
 <script>
+import SeenBy from "./SeenBy.vue";
 import messageMixin from "./messageMixin";
 
 export default {
   mixins: [messageMixin],
+  components: { SeenBy }
 };
 </script>
 <style lang="scss">