Add email list to email-prefs page

This was quite a big refactor to the EmailController as we tried multiple things that kept going wrong.
This seems to have gone right.

## Prove it
![email-prefes-d](https://cloud.githubusercontent.com/assets/31692/4090530/fab3b734-2f7d-11e4-81d0-ea857f14ae48.png)
![email-prefes-m](https://cloud.githubusercontent.com/assets/31692/4090531/fab946fe-2f7d-11e4-9cfc-43ec38c800ba.png)

![SPAM!](http://www.cloudways.com/blog/wp-content/uploads/spam.gif)
Can you not just move `api.user(userId, request.auth)` here, rather than binding it to `user` and then `u`?

i.e.,

```scala
(for {
  user <- api.user(userId, request.auth)
  subscriber <- api.userEmails(userId, idRequest.trackingData)
} yield {
  // etc
})
```