New responsive nav

- add a new switch for the new navigation redesign: ResponsiveNavSwitch
- add DOM structure for the new mega nav behind the above mentioned switch, this displays all sections and subsections, highlighting the current selection.

![screen shot 2014-06-25 at 18 26 08](https://cloud.githubusercontent.com/assets/1492162/3388879/f1675424-fc8d-11e3-855a-edf0d586579c.png)

![giphy](https://cloud.githubusercontent.com/assets/1492162/3388914/6cb87928-fc8e-11e3-98e9-055518c6a5d3.gif)


Is that TODO not relevant anymore?