RFC: Introduce basic colord integration

This merge request introduces a way to load the VCGT tag from an ICC color profile to the video card. It doesn't solve the color management problem on wayland per se. Applications still need to tag their surfaces with color space info, rendering intent, etc, so the compositor could perform conversions between the color space the surface is in and the display's color space.

Design-wise, the colord integration is implemented as a plugin. d-bus api is used to create colord devices and monitor color profile changes. After kwin has created a device, the user can change its color profile in Color Corrections KCM or via colord APIs.

One could argue that the compositor should provide a generic wayland protocol to set gamma ramps. However, since we will have to provide our own code path to upload LUTs anyway, the benefits of having such a protocol are unclear.

This is not a final solution, in fact it's a quick and dirty patch that I wrote last Saturday night. It would be great to hear the opinion of other kwin developers regarding whether the proposed design is sound or whether we should lean towards another option.

related #11