NiLearn Website - small tweaks for small phone screens

The carousel as well as the navbar behaves a bit badly on small mobile screens like the Motorola RAZR V8 for example:

![screenshot at 2013-09-12 10 47 54](https://f.cloud.github.com/assets/1378870/1129315/536aa230-1b88-11e3-949e-7ea523da2d1c.png)
![screenshot at 2013-09-12 10 48 05](https://f.cloud.github.com/assets/1378870/1129316/5868041c-1b88-11e3-8720-fb11a261efd7.png)


This is a little fix for that behaviour