Flatten threads: don't show reply button when appropriate

This CL also refactors the response interceptors to use the new
ThreadModel.

Fixed: twpowertools:160
Change-Id: I859e0fa1b8f5f4057bd66af3d167e4b21c6d12ed
diff --git a/src/models/Gap.js b/src/models/Gap.js
index 59e4882..8c380b2 100644
--- a/src/models/Gap.js
+++ b/src/models/Gap.js
@@ -1,6 +1,9 @@
+import ThreadModel from './Thread.js';
+
 export default class GapModel {
-  constructor(data) {
+  constructor(data, thread) {
     this.data = data ?? {};
+    this.thread = thread ?? new ThreadModel();
   }
 
   getCount() {