Support for Lab color space #3

I personally don't think Lab is a good choice for image processing and it is technically not a relative color space, complicating matters. HCY is much better suited for generating colors with perceptively uniform luminance. That said many devs are experimenting with it and finding a working formula can be very tricky, so just having it in libColorTool would simplify it.

It would also need functions that calculate what ranges are valid for each component given the other two components in order to be fully supported.