Adds a separator between nav-tabs

Fixes #408.

This adds a separator between the nav-tabs:
![screenshot 2014-07-09 22 46 28](https://cloud.githubusercontent.com/assets/5510679/3534260/0f74365a-07e5-11e4-90af-66febe3fd296.png)

The file tab.less was edited, and lessc was used to compile october.less to october.css