Improved user state methods

cc @fancyremarker

Improved convenience methods for tracking a user's sign up progress
Rubocop is complaining about these names. Feel free to ignore the `has_` warning. If you're going to change any of these, my suggestions for names would be:

* `has_account?`
* `subscribed?`
* `email_verified?`
* `subscribed_and_verified?`

Don't have terribly strong opinions though.