cleanup series of webxdc info messages (#3395)

* clarify webxdc reference wrt info-messages

* add from_id parameter to add_info_msg_with_cmd()

* flag webxdc-info-messages as such

* set from_id to sender for webxdc-info-messages

* test additional webxdc info properties

* do not add series of similar info messages

instead, if on adding the last info message
is already from the same webxdc and sender,
just update the text

* test cleanup of webxdc info messages series

* update changelog

* make clippy happy

there is no real complexity in the args,
so allowing one more arg is probably fine.

if really wanted, we can refactor the function in another pr;
this pr is already complex enough :)

* use cleaner function names and comments

* clarify CHANGELOG

src/mimeparser.rs

@@ -140,7 +140,11 @@ pub enum SystemMessage {
 
     // Sync message that contains a json payload
     // sent to the other webxdc instances
+    // These messages are not shown in the chat.
     WebxdcStatusUpdate = 30,
+
+    // Webxdc info added with `info` set in `send_webxdc_status_update()`.
+    WebxdcInfoMessage = 32,
 }
 
 impl Default for SystemMessage {