Set /Send subscriptions notifications/ /Publishing option/ defaults by content type

Issue Summary

The defaults for all the Publishing options can be set on the admin/content/types/CONTENT_TYPE/edit page. This should apply to Subscriptions, too.

We'll need three defaults, one each for:
— new nodes
— unpublished nodes (delayed creation at publication time)
— published nodes (update)

When unpublished nodes are published, we technically have an update, but semantically it's a (delayed) node creation.

As soon as #761260: Add a /Send subscriptions notifications/ option to the comment's Administration fieldset is implemented, we'll need another three options for the comments, so it makes sense to do that task first.