TODO

   1 Styles must be improved (full width for smartphones, ...)
   2 PGN text is not selectable (understand why?!)
   3 Change cursor when computer "think" (sablier)
   4 Tooltip text should fade (even when mouse stay on it, especially for small screens)
   5 Checkered stage 2: switch button at reserve position (or on top).
   6 Mode expert: game.js, button on top (with online indicator)
   7 Turn indicator on top too (black or white)