Remove parallax effect for mobile

HE site flows better without parallax. 
It keeps parallax effect for desktop.

There was an annoying bug when I use iPhone to see the site. It is also fixed.
![bug-he-site](https://f.cloud.github.com/assets/97197/1804336/f8b8d146-6c49-11e3-978a-371cb044e4ce.png)