Add a "To Top" link in a new footer viewlet.

Add link "To Top" in a new viewlet.
Styling is already done.
Translated to `German`, `French`, `Italian`.

![bildschirmfoto 2013-09-20 um 17 39 01](https://f.cloud.github.com/assets/7469/1181525/d32c707e-220a-11e3-8471-435359fcb83e.png)

@ninfaj