Improve member adding and excluding flow

Allow to exclude a member

Send emails to the member when it's excluded

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

lib/federation/activity_stream/converter/post.ex

@@ -35,7 +35,7 @@ defmodule Mobilizon.Federation.ActivityStream.Converter.Post do
       "name" => post.title,
       "content" => post.body,
       "attributedTo" => creator_url,
-      "published" => post.publish_at || post.inserted_at
+      "published" => (post.publish_at || post.inserted_at) |> DateTime.to_iso8601()
     }
   end