Integrate newsletter sign-up with FWP

[CrispinF]

FWP can be used to ask potential customers for their email and about their interests, and it would be nice if this could also allow them to sign up for news (or do so automatically), without that having to be a separate exercise (or having to write a custom submission handler). Perhaps this comes therefore as an extension to an "Email" question - if asking for the user's email, how about a new config option to either a) automatically sign them up for all configured newsletters in the site, or b) show them which newsletters they can sign up for? I would like to use the first option in a couple of real world examples, because the form instance is already explaining what's on offer.

[JosephMDavis]

I like this idea. We'll look at adding it soon.