Provide jQuery source map

Helps when debugging with Chromium, see https://stackoverflow.com/questions/18365315/jquerys-jquery-1-10-2-min-map-is-triggering-a-404-not-found and http://blog.jquery.com/2013/01/09/jquery-1-9-rc1-and-migrate-rc1-released/#sourcemaps for some more info about them.