Updated page to properly report spec-compliant gamepad API results

Chrome is [being updated](https://codereview.chromium.org/183313003/) to use the newest [Gamepad API spec](https://dvcs.w3.org/hg/gamepad/raw-file/default/gamepad.html), which is compatible with Firefox's implementation (Available in Firefox 28+). This patch allows the page to properly poll the new format while preserving backwards compatibility with the old one.

Other minor updates:
 * Added a border to the button states to indicate when "button.pressed" is true/false
 * Added field to display "gamepad.mapping" string. 

I would appreciate if you could deploy this to http://html5gamepad.com/ so that I have a reliable example site to point developers at when the new API lands. Thanks for putting this site together, by the way! It's been a godsend for testing Chrome!