Add a new generator and solver to KSudoku, based on published algorithms. The aim is to address and eventually close bug report 217925 and its duplicates 228614 and 237262, as well as overcoming some computational overheads of the current algorithms. In this version, the old and new generators are both available in the startup screen and can be easily compared. The old generator creates mainly easy puzzles, whereas the new implements a wide range of puzzle difficulties, namely Very Easy, Easy, Medium, Hard and Diabolical. The new generator is documented in file src/generator/sudokuboard.h and in other .h files in src/generator.