fix and refactor reviewers header (bug 890344)

**Notes:**

- Fix the queue switcher from colliding with the settings cog.
- Fix the effective mouseout area of the account-links dropdown to not overlap with other nav elements.
- Fix the header padding's width being set too large, causing white space on the right of the page.
- Factor out reviewers mobile and header styles into their own stylesheets, the reviewers stylesheet was getting messy.

![screen shot 2013-09-11 at 5 40 39 pm](https://f.cloud.github.com/assets/674727/1127687/fb19be8e-1b43-11e3-9561-f8d8612cd4a5.png)

![screen shot 2013-09-13 at 2 39 54 pm](https://f.cloud.github.com/assets/674727/1141817/1c150fec-1cbd-11e3-9473-b12b3bd1b39f.png)

![screen shot 2013-09-13 at 2 40 03 pm](https://f.cloud.github.com/assets/674727/1141818/1f0fc94e-1cbd-11e3-9ddd-c769f75309fa.png)