Do not hardcode NodeJS backend port in frontend

[JohannesOehm]

In src/public/hooks:socket.js:6 the port of the NodeJS-backend is hardcoded to 3231. Please make this function more intelligent, so that it discovers which port is actually used to serve the frontend static pages or omits the port from the socketUrl string if port 80 is used with http or 443 is used with SSL.