Registration overhaul

## TODO

- [ ] Redirect to library after subscribing w/ facebox of old "Thanks" page. Should say "Your account is now set up, which means that you can enjoy everything that Practicing Ruby has to offer. If you have any questions, please send an email to gregory@practicingruby.com."
-  [x] Inline validation for confirmation email form (Present and unique)
- [ ] Blog post reviewing the changes