Adding Variants

[SudokuMonster]

Added several variants visibleCellIndex and visibleCellSets are updated by calling changeVisibleCells. isVanilla() will be used throughout the code to minimizes un-necessary check for different variants when in vanilla sudoku mode. Disjoint groups is currently has each block position in a different colour. I'm hoping that I can use a B&W texturedPaint instead in the future.

Decided not to allow simultaneous "Extra groups" as I'm out of colours! All can be used from command line though