Add ability to set a default post expiry (#321)

[akkoma] / priv / repo / migrations / 20190325185009_create_notification_id_index.exs

defmodule Pleroma.Repo.Migrations.CreateNotificationIdIndex do
  use Ecto.Migration

  def change do
    create_if_not_exists(index(:notifications, ["id desc nulls last"]))
  end
end