feat: include 3 recent Message-IDs in References header

Do not include oldest reference, because chat members
which have been added later and have not seen the first message
do not have referenced message in the database.

Instead, include up to 3 recent Message-IDs.

src/receive_imf.rs

@@ -2683,7 +2683,6 @@ async fn get_rfc724_mid_in_list(context: &Context, mid_list: &str) -> Result<Opt
 ///
 /// If none found, tries In-Reply-To: as a fallback for classic MUAs that don't set the
 /// References: header.
-// TODO also save first entry of References and look for this?
 async fn get_parent_message(
     context: &Context,
     mime_parser: &MimeMessage,