Introduce comments below events

Also add tomstones

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/service/formatter/formatter.ex

@@ -34,7 +34,12 @@ defmodule Mobilizon.Service.Formatter do
 
   def mention_handler("@" <> nickname, buffer, _opts, acc) do
     case Actors.get_actor_by_name(nickname) do
-      %Actor{id: id, url: url, preferred_username: preferred_username} = actor ->
+      %Actor{preferred_username: preferred_username} = actor ->
+        link = "<span class='h-card mention'>@<span>#{preferred_username}</span></span>"
+
+        {link, %{acc | mentions: MapSet.put(acc.mentions, {"@" <> nickname, actor})}}
+
+      %Actor{type: :Person, id: id, url: url, preferred_username: preferred_username} = actor ->
         link =
           "<span class='h-card'><a data-user='#{id}' class='u-url mention' href='#{url}'>@<span>#{
             preferred_username