Add topic to rom info

Issue #59.

src/components/RoomInfo.vue

@@ -24,6 +24,7 @@
           }}</span>
         </v-avatar>
         <div class="h1">{{ roomName }}</div>
+        <div class="h3">{{ roomTopic }}</div>
         <div class="small">Created by {{ creator }}</div>
         <canvas class="qr" id="room-qr"></canvas>
       </div>
@@ -191,6 +192,13 @@ export default {
       return "";
     },
 
+    roomTopic() {
+      if (this.room) {
+        return this.room.topic;
+      }
+      return "";
+    },
+
     anyoneCanJoin() {
       // TODO: fix this! For now, just return true of we have a canonical alias.
       if (this.room && this.room.getCanonicalAlias() && this.room.getCanonicalAlias().startsWith('#')) {