🎉 Launch "flatten threads" feature

Fixed: twpowertools:153
Change-Id: I09eb246a4b6de130d5bed81cefe9109995aaf43b
diff --git a/src/static/_locales/en/messages.json b/src/static/_locales/en/messages.json
index 94fd093..7f6b213 100644
--- a/src/static/_locales/en/messages.json
+++ b/src/static/_locales/en/messages.json
@@ -179,6 +179,10 @@
     "message": "Reduce the whitespace in the Community Console and TW.",
     "description": "Feature checkbox in the options page"
   },
+  "options_flattenthreads": {
+    "message": "Show a toggle to enable/disable nested view in threads.",
+    "description": "Feature checkbox in the options page"
+  },
   "options_save": {
     "message": "Save",
     "description": "Button in the options page to save the settings"