Fix broken links on the website

This MR fixes some broken links on the website.

A link is still broken: https://gforge.inria.fr/projects/gtg/, but I don't know the new URL (has it been migrated ?).

web/header.html

-<div id="header" onclick="location.href='index.php'">
+<div id="header" onclick="location.href='index.html'">
 	<h1>Visual Trace Explorer</h1>
 </div>