This is a bit messy: The spec says that PCSXYZ and PCSLAB are the only
valid profile connection spaces -- except for DeviceLink profles, where
all data color spaces are valid.
So this uses the existing ColorSpace enum for profile connection spaces
instead of adding a dedicated enum, to not duplicate all the color space
parsing and printing code. That matches what the spec does, too.
This saves about 100 lines of code, at the expense of less type
safety -- but further down the line we probably want to be able to
compare data color spaces and profile connection spaces, so the type
safety would likely get in the way then. (But if not, we can change
things around once we get to that point.)
