Integrate the old KSudoku and the new generator/solver more closely.

Both now use the same data structures for puzzle and solution contents. The SKGraph class is now the central data-structure used by views, generator, solver, save file, load file and manual puzzle entry. It represents the type, size, shape and rules of a Sudoku puzzle, either in 2D or 3D, and has been streamlined and simplified. The PlainSudokuBoard, RoxdokuBoard and SamuraiBoard classes that inherited SudokuBoard (the generator/solver) have been deleted. SudokuBoard now works entirely by using SKGraph.