Change which task events the caller is emailed and pushed about [write]

Send email, push or both, each with only the kinds to change; the response holds all of them. email.marketing: false unsubscribes the caller's own address from marketing email, the same opt-out as the unsubscribe link in a marketing email; 409 no_email for an account without an address. Answers 503 not_available for task kinds until the platform's notification tables are in place.