Restore source code use via "download/get/*.js"

fixes #199 

The interesting commit with changes in `index.js` is this: https://github.com/SergioCrisostomo/website/commit/9bd1d80ef8faeb28227de9d8a0cda2bc85c0f13e, the other commit is a folder with all the old source files, copied from Google's CDN. It would also be an option to hot-link to Google, but then we would depend on third party for this functionality.