Bug 1130852 -Add opt-out notification for calendar integration - Thunderbird part. r=mkmellin

mail/app/profile/all-thunderbird.js

@@ -836,3 +836,6 @@ pref("mail.save_msg_filename_underscores_for_space", false);
 // Disable cache v2 since migration has not been done, it is pending in bug 1021843.
 pref("browser.cache.use_new_backend",       0);
 pref("browser.cache.use_new_backend_temp",  false);
+
+// calendar promotion status
+pref("mail.calendar-integration.opt-out", false);