Integrate ActiveJob / DeliverLater / GlobalID with Rails

WIP.
The whole issue started because I pointed out deserialization with GlobalID could raise `ActiveRecord::RecordNotFound`, which would lead to an infinitely requeued job on at least Sidekiq (https://github.com/rails/activejob/issues/25). After a little bit of discussion, loaning `rescue_from` from AC was suggested by @dhh because it would do the trick and be familiar to users.

I'm not married to `#rescue_from` and I agree that it introduces a couple of new issues. In the end, all I would really like is a way to handle those `RecordNotFound` errors that is straightforward and easy enough to be recommended to and used by less experienced AJ users who use it with GlobalID models.

If we're moving away from `rescue_from`, we're pretty much restarting that discussion. Do you have any input on the problem described there, any other ideas on ways to handle it?