feat: show reactions in summaries (#5387)

shows the last reaction in chatlist's summaries if there is no
newer message.

the reason to show reactions in the summary, is to make them a _little_
more visible when one is not in the chat. esp. in not-so-chatty or in
one-to-ones chats this becomes handy: imaging a question and someone
"answers" with "thumbs up" ... 

otoh, reactions are still tuned down on purpose: no notifications, chats
are opend as usual, the chatlist is not sorted by reactions and also the
date in the summary refer to the last message - i thought quite a bit
about that, this seems to be good compromise and will raise the fewest
questions. it is somehow clear to the users that reactions are not the
same as a real message. also, it is comparable easy to implement - no
UI changes required :)

all that is very close to what whatsapp is doing (figured that out by
quite some testing ... to cite @adbenitez: if in doubt, we can blame
whatsapp :)

technically, i first wanted to go for the "big solution" and add two
more columns, chat_id and timestamp, however, it seemed a bit bloated if
we really only need the last one. therefore, i just added the last
reaction information to the chat's param, which seems more performant
but also easier to code :)

src/chatlist.rs

@@ -416,7 +416,7 @@ impl Chatlist {
         if chat.id.is_archived_link() {
             Ok(Default::default())
         } else if let Some(lastmsg) = lastmsg.filter(|msg| msg.from_id != ContactId::UNDEFINED) {
-            Ok(Summary::new(context, &lastmsg, chat, lastcontact.as_ref()).await)
+            Summary::new(context, &lastmsg, chat, lastcontact.as_ref()).await
         } else {
             Ok(Summary {
                 text: stock_str::no_messages(context).await,