Store roadmap subscription status in Squeak!

[corywatilo]

For MVP, we're sending roadmap subscribers into Mailchimp.

If you're signed into Squeak!, you can subscribe without having to enter your email address. After clicking a subscribe button, the button is relabeled to Subscribe.

But after a refresh, the button returns to the original state, thus not reflecting subscription status.

Next step here would be to:

1. Record subscriptions on the Squeak! user record
2. Show subscribed status here, so it doesn't look like a bug that we didn't record it
3. Create a Subscriptions page in your Squeak! profile settings to allow you to view/manage subscriptions (2nd mockup here)