Show nav in footer

with JS:

![localhost 9000-320x320](https://cloud.githubusercontent.com/assets/867233/3875443/edde12d2-2151-11e4-89e7-1eccdb141769.png)
![localhost 9000-740x320](https://cloud.githubusercontent.com/assets/867233/3875441/eddc035c-2151-11e4-8177-1fa1ba21f2c6.png)
![localhost 9000-980x320](https://cloud.githubusercontent.com/assets/867233/3875442/eddc91d2-2151-11e4-9653-97103338d946.png)

Without JS:

![screen shot 2014-08-11 at 13 21 28](https://cloud.githubusercontent.com/assets/867233/3875455/2bf0fb7a-2152-11e4-9639-27a0ee64ee37.png)
![screen shot 2014-08-11 at 13 21 56](https://cloud.githubusercontent.com/assets/867233/3875456/2bf68752-2152-11e4-92df-fa4faa73a0d4.png)
I think that should stay as it was, to decouple completely navigation structure from what's in it (and avoid having a `navigation__expandable` into sections.scala.html.