feat(app-socket.io): build socket.io into vendor.js

Changes:
- Move socket.io script tag inside vendor.js build
- Add `node_modules` to vendor script locations
- Change socket.io path to `/socket.io-client` in serve and client
- Will not serve socket.io.js when server is ran in `production` env
- Add `socket.io-client` to package.json for a more consistent build