Add website url to user

I thought it could be useful to be able to fill in a website url (may it be company related or not) in one's profile.

![profile view](https://f.cloud.github.com/assets/236461/1947612/39843b98-805e-11e3-82f7-0d25a60a4f91.png)

![profile edit](https://f.cloud.github.com/assets/236461/1948111/db03fa12-807c-11e3-85fa-ffb9333884e1.png)