Set timestamps for system messages

Previously system messages were always added to the end of the chat,
even if the message triggering them was sent earlier.  This is
especially important for messages about disappearing timer reset
triggered by classic email messages, as they should be placed right
after the message resetting the timer.

src/e2ee.rs

@@ -178,7 +178,9 @@ pub async fn try_decrypt(
     let mut signatures = HashSet::default();
 
     if let Some(ref mut peerstate) = peerstate {
-        peerstate.handle_fingerprint_change(context).await?;
+        peerstate
+            .handle_fingerprint_change(context, message_time)
+            .await?;
         if let Some(key) = &peerstate.public_key {
             public_keyring_for_validate.add(key.clone());
         } else if let Some(key) = &peerstate.gossip_key {