ready: Wait for other ready callbacks before marking app loaded.

This is needed not because the DOM isn’t ready here (we’re in a
<script defer>), but because we want to wait an asynchronous tick
until after all the other callbacks that waited an asynchronous tick
for the DOM to be ready.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

static/js/ready.js

@@ -1,3 +1,5 @@
 import $ from "jquery";
 
-$("#app-loading").addClass("loaded");
+$(() => {
+    $("#app-loading").addClass("loaded");
+});