Permute a sudoku.
Y = sudoku_permute ( X )
a 9x9 matrix
a permuted 9x9 matrix.
Generates a permuted sudoku Y from the sudoku X by performing permutations of rows within a band, columns within a band and bands (a set of 3 rows inside a block is a band). This way, X and Y are within the same class and, if X is a valid sudoku, then Y is a valid sudoku.