Update Web Platform Docs & Provide Update Script

Finally got a fix for #6027.
Updated `css.json` to include the latest data and wrote a Node script (`update-docs.js`) for further updates.
The script will only set the values we actually need, which keeps the file as small as possible.

The only remaining issue (which has existed before): The values are not in any useful order.
Since you already include lodash.unescape, why not depend on lodash itself and use it's forEach method?