"Sign me up for a bunch of junk" checkboxes on registration

[stuartpb]

Seems like this'd be a nice thing to profile. You could use it to make an extension that auto-unchecks these whenever you register an account somewhere (though it'd need better registration-page detection than what the current schema affords to be really robust, due to the design of url being about redirection in-points over matching patterns).

[stuartpb]

Example: https://auth.zappos.com/register has checkboxes for a mailing list (checked by default) and a "rewards" program (unchecked by default).

[stuartpb]

Also, Zappos has that Rewards checkbox on their login form, too.

[stuartpb]

This could be incorporated into the stuff that's being drafted in #176, but I'm not sure the proper model for junk like this is so cut-and-dry as of yet, so I'm putting this on the "future" milestone while the other is on "v0.1.0".

[stuartpb]

I think this should be fields under registration.form.subscribe, like registration.form.subscribe.offers.checkbox: checked.