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/web/cache/cache.ex

@@ -17,6 +17,7 @@ defmodule Mobilizon.Web.Cache do
     Enum.each(@caches, &Cachex.del(&1, "actor_" <> preferred_username))
   end
 
+  defdelegate get_actor_by_name(name), to: ActivityPub
   defdelegate get_local_actor_by_name(name), to: ActivityPub
   defdelegate get_public_event_by_uuid_with_preload(uuid), to: ActivityPub
   defdelegate get_comment_by_uuid_with_preload(uuid), to: ActivityPub