Replace outdated NTSC RGB luma factors with sRGB ones

[gonzzza007]

Replace outdated NTSC RGB luma factors with sRGB ones. Here's some additional info:
http://www.brucelindbloom.com/index.html?WorkingSpaceInfo.html

[alalek]

Actually this patch breaks a lot of existed pre-trained cascades, datasets and other models.
In general you should extend, and not break existing functionality.