Made the logo and header nicer on smaller screens

The logo was being cut off between 768px and 1000px wide screens:

![Screen Shot 2013-04-19 at 00 12 16](https://f.cloud.github.com/assets/1060/399746/8fbc28ea-a87d-11e2-89c0-9e07c44b8097.png)

Fixed that up to use a smaller logo all the time and reduced the overall header height as well:

![Screen Shot 2013-04-19 at 00 11 44](https://f.cloud.github.com/assets/1060/399749/b4e394dc-a87d-11e2-94a9-7dd302d1fd3f.png)

![Screen Shot 2013-04-19 at 00 11 50](https://f.cloud.github.com/assets/1060/399750/b9c5e14e-a87d-11e2-91fe-77a54e542585.png)