[nightcolor] Expose transition timings to d-bus
Summary:
These timings can be useful for the night color applet. For example, it
could show "Next transition will start at XXX" or something like that.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D26666