Socket.io server for real-time chat events in the game

[metalalive]

Note

• current events implemented in the socket.io server
  • init , join a room of specific game ID
  • deinit , leave a room of specific game ID
  • chat, chat with other players of the same room
• the events init and deinit can be reused for synchronizing game state from HTTP / REST server to each client.
• this PR completes first portion of the TODO list , see my previous comment

c.c. @wingtkw Wing, if you can spend time reviewing the PR today or tomorrow, please let me know , then I can also send review request to you , thanks