serve local Node server in `launch` for projects on user's local filesystem

[cvan]

currently, only URLs are allowed. we should also support spawning a local server if a local file path is passed as the URL/path.

example usage:

• fxr launch ~/Projects/my-webvr-demo/
• fxr launch --url=~/Projects/my-webvr-demo/
• fxr launch --path=~/Projects/my-webvr-demo/
• fxr dev ~/Projects/my-webvr-demo/
• fxr dev --url=~/Projects/my-webvr-demo/
• fxr dev --path=~/Projects/my-webvr-demo/
• stretch goal: fxr dev (then prompt for path)

this should help a ton with local development.

1. npm i --save live-server live-server-https

2. then add something like this to commands/launch.js:

   const tls = require('tls');
   const https = require('live-server-https');
   const PORT = SETTINGS.dev_port || 8080;
    const server = tls.createServer(https, (socket) => {
     console.log(`Server connected: ${socket.authorized ? 'authorized' : 'unauthorized'}`);
     socket.write('Greetings!\n');
     socket.setEncoding('utf8');
     socket.pipe(socket);
   });
   server.listen(PORT, () => {
     console.log(`Running local server on port ${PORT}`);
   });