website: new website !

A new menu and logo for the website, also some of the contents has been
reworked.

This patch also removes files that are no longer used, like the old
stylesheet and a few pages. The content of theses pages has mostly been
merged in other pages or was redudant with the manual.

[Thomas: integrate a few typo fixes noticed by Thomas De
Schampheleire]

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>