more levels! and undo

100 levels!

I reorganized the levels, now

10 - 3x3x3 levels that should show the mechanics and slowly introduce the logic behind the game

30 -  3x3x3 levels with increasing difficulty

50 - 4x4x4 levels with increasing difficulty

10 - 5x5x5 levels with increasing difficulty

Following feedbacks, I implemented an undo button to go back to the previous positions

Until I implement a menu system with  the possibility to choose the level, on pc is possible to skip levels using 'p'