Changed KCM to launch in system settings
KCM used to open in a separate window, changed that behaviour to launch in system settings when launched via the plasmoid.
As opposed to the change in daemon.cpp file suggested in the #446337 report, this change is implemented in the plasmoid, which is loaded only in a Plasma session. Hence, env check is not strictly necessary.
Tested to work on OpenSUSE TW, replaced system's plasmoid folder with plasmoid from build output.