Fix responsive header

# Before

When the screen width is less than around 960px the bootstrap style collapse ui will show up, but it's not very elegant.
![screen shot 2013-06-06 at 9 40 21 pm](https://f.cloud.github.com/assets/184520/617908/53351b94-cea6-11e2-8079-899002d53e17.png)

# After
I removed the collapse ui entirely, and added a responsive css to hide the user name and narrow down the padding of the left ui.

The iPhone is just for a demo :trollface: 
![screen shot 2013-06-06 at 9 38 08 pm](https://f.cloud.github.com/assets/184520/617912/7826cf92-cea6-11e2-9dd3-e6d645a7304d.png)