Website update

The ubos.net website has been updated reworked in many ways. Here is a non-exhaustive summary of changes:

• Simpler front page that clearly lists the UBOS components and is more to the point.
• The UBOS Mesh project was renamed to UBOS PeerGraph a while ago; now the website reflects that.
• The document hierarchy is now clearer and easier top maintain.
• The HTML/CSS layout has been improved. Hope you like it.