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

Changes:
- Move socket.io script tag inside vendor.js build
- Add `node_modules/socket.io/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
We moved the socket.io script tag inside the usemin build block so it will get included in vendor.js. We add `node_modules` to the search glob for the build, and change the path to `socket.io-client/...` since we install `socket.io-client` as a dependency. That way the paths all line up nicely and we still use the same script that socket.io would serve.