Summary:
Move from krdb (see D28070) with some refactorings.
Depends on D28070

Test Plan:
{F8178998}

This is how I got it to work, improvements to the process are appreciated
# Apply D28070
# Compile breeze-gtk and then copy `$PREFIX/kde/usr/share/themes/Breeze` to `/usr/share/themes` (replacing the existing Breeze (make a backup)). This is needed because Breeze-Gtk recently changed its color definitions names, which are used in this diff. Old Breeze-Gtk uses different ones and therefore the coloration won't work.
# Run systemsettings and reapply Breeze theme from Application Style KCM
# Restart `kded5`
# Go to colors KCM, open it side by side with GTK3 applications (preferably Gedit NOT Nautilus or Lutris (those ones are kept open if you press cross in headerbar))
# Change the color scheme.
# The application must change the colorscheme

Reviewers: cblack, #plasma, ngraham

Reviewed By: cblack, #plasma, ngraham

Subscribers: ndavis, ngraham, davidre, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28072