Multi-Variant Sudoku App

Implementations currently included:

helper notes (pencil-marks / notations)
grid square coloring (9 colors -- including white)
long diagonal lines (with checking for unique values)
arrows (8-directional -- no checking)
thermometers (with checking for normal or broken)
anti-knight checking
anti-king checking
anti-queen checking (using any specific value)
killer cages (unique value checking only -- no sums)
gray cells (no checks yet)

Thermometers, Killer cages and Magic squares (once implemented) can be removed by:
>Selecting head grid cell of object
>Pressing same as what created the object
(puzzle cannot be locked in solve mode)