Cleaned up the project folder structure, and renamed files

I cleaned up the project a little and fixed various bugs.

1. I renamed the node server JS file to server.js
2. I created folders img, css and js under /public.
3. I renamed the groupChatSocket.js file to GroupChatClient.js and moved it under /public/js.
4. I moved the CSS file style.css to /public/css.
5. I changed the paths to the scripts and CSS stylesheet in index.html.
6. I moved the script tags in index.html into the HEAD of the html document.
7. I changed the port number on which SockJS listens to 3001, to prevent it from clashing with Express which listens on port 3000.
8. I changed the ports on the server which the client connects to from 3000 to 3001.