Add warning message when using old thread design

In threads which are using nested replies, a warning will be shown if
the user has enabled the old thread design to notify them that they
won't work properly.

Fixed: twpowertools:139
Change-Id: I393ac187fef22a4c5f062bf99d84c373011d514b
diff --git a/templates/manifest.gjson b/templates/manifest.gjson
index d649b71..e3eb47f 100644
--- a/templates/manifest.gjson
+++ b/templates/manifest.gjson
@@ -98,6 +98,7 @@
         "css/ui_spacing/shared.css",
         "css/ui_spacing/console.css",
         "css/ui_spacing/twbasic.css",
+        "css/thread_page_design_warning.css",
 
         "communityConsoleMain.bundle.js.map",
         "communityConsoleStart.bundle.js.map",