Huge improvements everywhere, move history and hint display where touched, the GameScreen now has better (and functional) statistics.

Fixed a really evil bug: One was not able to make a move in the 'I' column before simply because GnuGo does not use the column 'I', it jumps from 'H' to 'L', strange beast.

This forced an GameScene update and changes to GoEngine (about checking valid moves and asserts).
MainWindow got another action for editing boards, this will be brought to live in a future update.