Unsubscribe usability improvements

Unsubscribing from an email used to be a single click process. Turns out that it's really just a little too easy to hit the "Stop Receving..." links accidentally, so we've inserted an extra confirmation page for users to validate their removal request. So now it's two clicks, but the risk of accidentally removing oneself is dramatically lower, and a lot more usable - especially for the "Stop all link" which deletes all subscriptions in one fell swoop.