Allow users to subscribe/unsubscribe from Product Updates

After lots of hard work behind the scenes, we are now ready to releasing lots of exciting new features in response to the user feedback we receive.

In order to make our users aware of what's changing we plan to start sending out Product Updates via email and WhatsApp.

Although we don't strictly consider this "marketing", we also feel it's fair to give our users the opportunity to unsubscribe from this sort of update. So we've made it possible to unsubscribe (or re-subscribe) to Product Updates via the Account Settings screen.