0029847: Visualization, Image_Diff - Tolerance is not effective for 24/32bit image...

0029847: Visualization, Image_Diff - Tolerance is not effective for 24/32bit image formats

Image_Color - removed semibroken summ/difference operators.
Image_Diff now uses signed integer for computing differnce between ubyte3 components;
properly compare squared tolerance.

Image_Diff - dropped declaration of Image_ColorXXX24.
RGB color difference is now computed using Chebyshev distance instead of Euclidean distance
Image_PixMap - added methods RawValue()/ChangeRawValue() returning a pointer
to image where specified pixel data is defined.