Send Notifications when participation approval

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

priv/repo/migrations/20200605154921_add_notification_pending_participation_to_settings.exs

@@ -0,0 +1,9 @@
+defmodule Mobilizon.Storage.Repo.Migrations.AddNotificationPendingParticipationToSettings do
+  use Ecto.Migration
+
+  def change do
+    alter table(:user_settings) do
+      add(:notification_pending_participation, :integer, default: 5)
+    end
+  end
+end