Revert "feat!: remove features related to the old thread page view"

This reverts commit 879d44aef99524c84719d91c628e772fba9335cb.

Reason for revert: It turns out the old reply editor can still be used
in the new thread page view by pressing the "R" key, and this can/will
make the CC communicate with the draft endpoints to save/retrieve
information.

Apart from this, some PEs were using the "old thread page" option as
well, even if it doesn't load all replies.

Finally, this revert also contains some changes to the modifications to
the data startup object so they work correctly (since now we have to use
StartupDataStorage, otherwise changes might not be saved).

Bug: twpowertools:124
Change-Id: Ie8153b9c8ef150b2417cb19b73bde0a5593876e2
diff --git a/src/contentScripts/communityConsole/start.js b/src/contentScripts/communityConsole/start.js
index f890bd0..64bc2a0 100644
--- a/src/contentScripts/communityConsole/start.js
+++ b/src/contentScripts/communityConsole/start.js
@@ -2,8 +2,13 @@
 import {getOptions} from '../../common/options/optionsUtils.js';
 
 import FlattenThreadsReplyActionHandler from './flattenThreads/replyActionHandler.js';
+import ThreadPageDesignWarning from './threadPageDesignWarning.js';
 
 getOptions(null).then(options => {
+  // Initialized here instead of in main.js so the first event is received if it
+  // happens when the page loads.
+  window.TWPTThreadPageDesignWarning = new ThreadPageDesignWarning();
+
   if (options.uispacing) {
     injectStylesheet(chrome.runtime.getURL('css/ui_spacing/shared.css'));
     injectStylesheet(chrome.runtime.getURL('css/ui_spacing/console.css'));