Integraded theme shop button in main menu
Added buying themes functionality
Updated Settings menu to include only the unlocked themes

Need to rewrite how the bought themes are stored. Because currently it is in an embedded resource. But you can unfortunatly not edit them so I need to find an other way

also setup for other parts of the shop

not done yet tho

doet fancy file read and write dingen
slaat settings and money op enzo
moet m nog laten werken met de settingsform enzo maar de basis is er

- 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

very cool