Dev environment updates

[beejunk]

I was looking to help with Shin KGS, and ran into issues getting the local development environment working. This PR adds the changes I made to get these issues resolved. These changes are:

• Updated node-sass and react-scripts to their latest versions. The older versions would not run in an Ubuntu 20.04 environment.
• Updated the main CSS import to point directly to the SCSS file. react-scripts will automatically build SCSS files if node-sass is present, so there's no need to do that manually.
• Added a Vercel (used to be now.sh) serverless-function to proxy KGS requests. This allows the Vercel preview deployments to work. Since Vercel has removed full-stack Node support in favor of a serverless architecture, the original proxy server setup no longer works. You can see this when visiting https://shinkgs-master.now.sh/ - the proxy requests are now returning 404 errors.
• Switch the local dev proxy to run through the Webpack dev server. This allows proxying to the KGS server without using HTTPS (and without needing to add a certificate exception in your browser).
• Update README accordingly.

[beejunk]

Whoops, I accidentally committed a package-lock.json file! I've amended the commit to remove that file.

Vercel deploy of these changes can be seen here: https://shinkgs.ectopod.vercel.app