undo staged move / options for move submission

[merowin]

Feedback from the forum: https://forums.online-go.com/t/game-setup-parallel-fractional-go-game-3/50336/4

For parallel move variants it would be nice to be able to undo the staged move(s).

OGS has options for how to submit a move: single click / two clicks / submit button. So we could also think about move submission systems alternative to "single click".

[JonKo314]

A submit-move-feature would be nice for all variants.

To undo staged moves I'd suggest introducing a new special move for that. It would be possible to send a move again to undo it, but that could be a bit dangerous, if moves are submitted more than once by accident.