Added JS engine colour stripe to platform headers.

Now, platforms' table `<th>` elements have a thin colour strip denoting their engine. Colours have been set for Trident (IE), SpiderMonkey (Firefox/Rhino), JavaScriptCore (Safari, Phantom, WebKit), V8 (Chrome, Opera, Node), Carakan (Opera 12) and KJS (Konqueror). This allows browsers versions to be more easily visually identified, as well as providing context to e.g. the similarity of WebKit and iOS.

Also, this fixes a bug where the platform type headers stopped being bold in the previous CSS pullreq.