With Wayland KWin needs to provide certain services, which were provided
before that by the Xserver. One of these is gamma correction, which includes
the - by many people beloved - functionality to reduce the blue light at
nighttime. This patch provides the KWin part of that. It is self contained,
but in the end will work in tandem with a lib in Plasma Workspace and a KCM
in Plasma Desktop, which can be used to configure Night Color.

* Three modi:
** Automatic: The location and sun timings are determined automatically
   (location data updates will be provided by the workspace)
** Location: The sun timings are determined by fixed location data
** Timings: The sun timings are set manually by the user
* Color temperature value changes are smoothly applied:
** Configuration changes, which lead to other current values are changed
   in a quick way over a few seconds
** Changes on sunrise and sunset are applied slowly over the course of few
   minutes till several hours depending on the configuration
* The current color value is set immediately at startup or after suspend
  phases and VT switches. There is no flickering.
* All configuration is done via a DBus interface, changed values are tested
  on correctness and applied atomically
* Self contained mechanism, speaks directly to the hardware by setting the
  gamma ramps on the CRTC
* Currently working on DRM backend, extensible to other platform backends in
  the future
* The code is written in a way to make the classes later easily extendable to
  also provide normal color correction, as it's currently done by KGamma on X

Test Plan:
Manually with the workspace parts and added integration tests in KWin using
the virtual backend.

BUG:371494

Reviewers: #kwin, graesslin

Subscribers: kwin, plasma-devel, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D5928