css tweaks to the new tab view

Some tweaks to the css for the new tab view:

 * change to use the same font as in the files view. There were too many different fonts on the screen - it was a bit jarring.
 * tweak the close button to be closer to the bootstrap default
 * remove the underline decoration - the tab header seemed busy, and the cursor change gives the user a good enough indication that the tab is actionable

![screen shot 2013-11-15 at 12 05 22 pm](https://f.cloud.github.com/assets/1269969/1553287/4e7e78ec-4e31-11e3-8866-1b0c68e84336.png)