TODO

   1 Styles must be improved (full width for smartphones, selectable text for PGN...)
   2 Tooltip text should fade (even when mouse stay on it, especially for small screens)
   3 Checkered stage 2: switch button at reserve position.
   4 If a played disconnect right after opponent sent a move, it might be never received: secure this
   5 Think about non-conventional variants with 2 kings for example: undercheck highlight?
   6   --> underCheck should return a vector in this case. Adapt.
   7     --> incheck should be an array of squares, in general. Think AntiKing