0028876: Tests, Image_Diff - the image difference is unavailable for test case bugs...

0028876: Tests, Image_Diff - the image difference is unavailable for test case bugs vis bug28205_1

Quantity_ColorRGBA - added method SetValues().
Image_PixMap::PixelColor() now returns Quantity_ColorRGBA instead of Quantity_Color.
Image_PixMap::SetPixelColor() now takes Quantity_ColorRGBA instead of NCollection_Vec4<float>.

Image_Diff has been improved to support Image_Format_Gray.
Image_Diff::SaveDiffImage() now saves image difference
in Image_Format_Gray format to reduce size of image file.

Image_Diff now uses TColStd_HPackedMapOfInteger instead of
TColStd_MapOfInteger with manual memory allocation.