Finish webhook API callback and remove unneeded demo app

labs/bbb-callbacks-demo/app.js

labs/bbb-callbacks-demo/package.json

labs/bbb-callbacks-demo/public/stylesheets/style.css

labs/bbb-callbacks-demo/routes/index.js

labs/bbb-callbacks-demo/routes/user.js

labs/bbb-callbacks-demo/views/index.jade

labs/bbb-callbacks-demo/views/layout.jade

labs/bbb-callbacks/app.js

labs/bbb-callbacks/package.json