Add fid to Feed

Author: szuperaz

src/StreamFeed.ts

@@ -1,3 +1,7 @@
 import { FeedApi } from './gen-feeds/feeds/FeedApi';
 
-export class StreamFeed extends FeedApi {}
+export class StreamFeed extends FeedApi {
+  get fid() {
+    return `${this.group}:${this.id}`;
+  }
+}