TODO

   1 Allow to navigate in game after it's over (back/play)
   2 For animation, moves should contains "moving" and "fading" maybe...
   3 (But it's really just for Magnetic chess)
   4 setInterval "CRON" task in sockets.js to check connected clients
   5 (every 1hour maybe, or more)
   6 Button to show all pieces that can move (next to expert mode; change icons)
   7 Some bots are very weak, others quite slow...