jQuery library to use Google CDN-hosted version

Update jQuery library to use Google CDN-hosted version which is faster/cheaper. (source: http://encosia.com/3-reasons-why-you-should-let-google-host-jquery-for-you/).

Used local fallback technique suggested by HTML5boilerplate (source: https://github.com/h5bp/html5-boilerplate/blob/master/index.html )