kludge: rename sl.png to favicon.ico

and host it on libreboot.org/ instead of av.libreboot.org/

the PNG "light" libreboot logo is well-optimized, and still opens properly in
most browsers even if named favicon.ico. the icon is going to be loaded on
pages anyway. having a separate favicon.ico adds an extra http request, which
causes seconds of lag on some connections

so make sl.png the favicon, and use that in the img tag on pages

site/template.include

@@ -65,7 +65,7 @@ $if(title)$
 <header>
 <div class="title">
 <p class="title-logo">
-<img class="title-logo" alt="" src="https://av.libreboot.org/logo/sl.png" />
+<img class="title-logo" alt="Libreboot logo" src="/favicon.ico" />
 </p>
 <h1 class="title">$title$</h1>
 </div>