Add a mark stating if we should start with left or right lever

[gemerat1]

Hello, In the physical game, there is a specific piece that is added to the left or right lever, that states that you should press that lever (and not the other one) to start. It seems that this indication is not present in the simulator. When trying to reproduce the initial board state and saving the puzzle in the "before" mode, it would be great to have this information. Therefore, the kid uploading the "before" state can try to complete the puzzle, and know which lever he will need to start to test if he has succeeded. It could be as simple as adding a peg below each lever, and a new "Start" piece to plug on that peg. And thank you for this admirable piece of work !