Muted `nohavemail` sprite

The `nohavemail` sprite is very dark for not having mail. Since there is no action, it should be muted and more in the background. This change aligns with reddit's muting of the `nohavemail` sprite as well.

Current `nohavemail`:

![Current `nohavemail` screenshot](https://cloud.githubusercontent.com/assets/902488/4778452/b547d76c-5beb-11e4-97d7-7ee3321f0a21.jpg)

Suggested `nohavemail`:

![Suggested `nohavemail` screenshot](https://cloud.githubusercontent.com/assets/902488/4778454/ca27978a-5beb-11e4-80f7-372ba95fbdf9.jpg)

Reddit's `nohavemail`:

![Reddit's `nohavemail` screenshot](https://cloud.githubusercontent.com/assets/902488/4778455/dc038374-5beb-11e4-9139-67402049d5ef.jpg)

Reddit's `havemail`:

![Reddit's `havemail` screenshot](https://cloud.githubusercontent.com/assets/902488/4778458/e63f758c-5beb-11e4-9434-e61c24a59bb5.jpg)