Support for more color spaces

[FiratUsta]

As it stands chromora only supports RGB, HEX and HSV color. While this should be "enough" for most use cases, adding support for more color spaces would expand the usability of the app to more uses and niches. Currently thinking support for at least the following color spaces should be added:

• RAW (RGB between 0 and 1, useful for shader work and probably more niches I don't know about.)
• HSL (Useful anywhere, starting to replace HSV in pretty much every other program I use)
• HWB (Useful for web, support coming with CSS 4)
• CMYK (Useful for print)

This would require a complete overhaul of the interface, and (possibly) the color back-end, which might end up breaking backwards compatibility so I'll put this into 3.x for now. Initial thought is to have HEX be the mainstay and let the user select a second (and maybe a third just like the current implementation) color space to work with (with sane defaults!)