[FIX] [IMP] mail: improved reply-to computing.
- mail_message: call get_message_reply_to even if no model / res_id, because the catchall has to be used if defined.
- mail_thread: better management of aliases and catchall alias. Moreover when giving a default, it is used as it is and not doc name <default>.
[FIX] mail, email_template: fixed tests to match the new reply-to implementation.