general updates

- TileClick and TileInput are now bool that return True if board is solved after input, false otherwise (so invalid or incomplete)
- virtual IsBoardSolved is called by TileClick and TileInput to verify board.
- removed some unused Board methods and added virtual hint method
- fixed impossible 4x4 sudoku generation
- improved solvability of sudoku
- changed draw method of sudoku to draw color givens and inputs differently
- hidden updatebutton
- added win method in puzzleform that runs when board is solved