imap: do not treat messages without Message-ID as duplicates

Message-IDs are now retrieved only during fetching and saved into imap
table. dc_receive_imf_inner does not attempt to extract the Message-ID
anymore.

For messages without Message-ID the ID is now generated in
imap::fetch_new_messages rather than dc_receive_imf_inner,
so the same ID is used in the imap table (maintained by the imap
module) and msgs table (maintained by dc_receive_imf module).

Message-ID generation based on the Date, From and To field hashing has
been replaced with a simple dc_create_id() to avoid retrieving Date,
From, and To fields in the imap module, as it's hard to test that it
stays compatible between Delta Chat versions in this module. This
breaks jump-to-quote for quoted messages without Message-ID, which is
not critical.

Also prefetch X-Microsoft-Original-Message-ID, so retrieval of
duplicate messages with X-Microsoft-Original-Message-ID can be skipped
like it is done for messages with Message-ID header.

src/mimeparser.rs

@@ -1138,7 +1138,7 @@ impl MimeMessage {
         }
     }
 
-    pub fn get_rfc724_mid(&self) -> Option<String> {
+    pub(crate) fn get_rfc724_mid(&self) -> Option<String> {
         self.get_header(HeaderDef::XMicrosoftOriginalMessageId)
             .or_else(|| self.get_header(HeaderDef::MessageId))
             .and_then(|msgid| parse_message_id(msgid).ok())