Speed up username display in header

Display username as soon as possible, as the first item in the header.

Not sure that's the right way to do it at all, though.

![screen shot 2014-07-28 at 13 27 51](https://cloud.githubusercontent.com/assets/85783/3724274/753db9e8-167c-11e4-9b21-622b3d73274f.PNG)
![screen shot 2014-07-28 at 13 25 22](https://cloud.githubusercontent.com/assets/85783/3724276/7b4ca6f0-167c-11e4-928b-f48bc2de5db7.PNG)

![ ](http://gifs.joelglovier.com/lolwat/wtf.gif)
@gklopper The [conversation here](https://github.com/guardian/frontend/pull/5249/files#r15512113) explains why.