Support for Null Moves

[chessnagar]

Hi Alf:
Another feature that you can consider is to support NULL moves, this will be very helpful in explaining the plans/threats/piece placements in a position.

Thanks
ChessNagar

[alf]

Null move support has been added in the chess parser(PHP Pgn Import), but not in the GUI yet. It's already on my trello board of things to do