TF-3413 Support Reply to list for email

model/lib/email/email_action_type.dart

@@ -1,6 +1,7 @@
 
 enum EmailActionType {
   reply,
+  replyToList,
   forward,
   replyAll,
   compose,

model/lib/email/email_property.dart

@@ -24,4 +24,5 @@ class EmailProperty {
   static const String references = 'references';
   static const String headerUnsubscribeKey = 'List-Unsubscribe';
   static const String headerSMimeStatusKey = 'X-SMIME-Status';
+  static const String headerListPostKey = 'List-Post';
 }