Put back Bootstrap 2 nav-list styles

* `nav-list` is a Bootstrap 2 design pattern heavily used in Publisher, Panopticon and others. Put back the styles for backwards compatibility when upgrading to Bootstrap 3, to avoid substantial redesign.
* Include examples in style guide, with warning about use of the pattern
* Clean up style guide visited/normal link hrefs using variables

![screen shot 2014-06-09 at 13 05 20](https://cloud.githubusercontent.com/assets/319055/3216337/b6fbf428-efce-11e3-87a4-2ee5766b4b31.png)

come to think of it, it might be more a bit more railsy to define these as helper methods in `ApplicationHelper`, rather than in the controller