prefer X-Microsoft-Original-Message-ID, if set

outlooks SMTP-server change the Message-ID of messages
and put the original Message-ID to X-Microsoft-Original-Message-ID.

the changed Message-ID has some issues:

- outgoing messages with bcc_self enabled are shown twice
  as the self-copy got the changed Message-ID while the database uses
  the original one

- read receipts do not work as they refer to the changed message id

- in general, sender and recipient see different Message-IDs

the issues can be fixed by

(1) let all receivers use the original Message-ID

	this is what this pr is doing
    and this should fix all issues with delta-to-delta communication,
	including groups, group-images etc.
    there may be issues left in communication
	with other MUAs as they are using another Message-ID.

(2) ftr: updating the Message-ID in the database of the sender to the new one

	this requires bcc_self always enabled (which is not the case)
    and may also result easily in race conditions
    (Bob answers before Alice sees its self-sent message),
    however, has the advantage of better compatibility with other MUA.

if needed, the compatibility with other MUA could be improved by remembering
both Messages-IDs, maybe we could treat the modified as References or so,
however, i think, this could be part of another PR if we know better about
real, in the wild issues.

src/mimefactory.rs

@@ -514,12 +514,6 @@ impl<'a> MimeFactory<'a> {
             ));
         }
 
-        // we could also store the message-id in the protected headers
-        // which would probably help to survive providers like
-        // Outlook.com or hotmail which mangle the Message-ID.
-        // but they also strip the Autocrypt header so we probably
-        // never get a chance to tunnel our protected headers in a
-        // cryptographic payload.
         unprotected_headers.push(Header::new(
             "Message-ID".into(),
             render_rfc724_mid(&rfc724_mid),