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>

test/federation/activity_pub/transmogrifier/undo_test.exs

@@ -39,7 +39,7 @@ defmodule Mobilizon.Federation.ActivityPub.Transmogrifier.UndoTest do
 
       assert data["type"] == "Undo"
       assert data["object"]["type"] == "Announce"
-      assert data["object"]["object"] == comment.url
+      assert data["object"]["object"]["id"] == comment.url
 
       assert data["object"]["id"] ==
                "https://framapiaf.org/users/peertube/statuses/104584600044284729/activity"