Replace our use of 'gamut' with 'primaries'. One is the axes of the
color space, the other the volume of representable values. For the
currently supported color spaces those are mostly equivalent, but when
we later add support for scRgb, this would be misleading as it has the
same primaries as sRGB but a much wider gamut, and we would like to use
the same primaries/"gamut" id for it.
Also few people would know what "the sRGB gamut" is, but
"the sRGB primaries" is easily googable.
Change-Id: I3348ccaae27a071ec77a4356331b9bbbf92e0d19
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>