Getter for last thread reply (#2015)

src/models/thread.ts

@@ -105,6 +105,15 @@ export class Thread extends EventEmitter {
         return this.timelineSet.findEventById(eventId);
     }
 
+    /**
+     * Return last reply to the thread
+     */
+    public get lastReply(): MatrixEvent {
+        const threadReplies = this.events
+            .filter(event => event.isThreadRelation);
+        return threadReplies[threadReplies.length - 1];
+    }
+
     /**
      * Determines thread's ready status
      */