Import kcmshell from kde-cli-tools

Task: https://phabricator.kde.org/T14427

Test Plan: Run the executable from the build dir: ./bin/kcmshell6 $HOME/kde/build/kcmutils/bin/fakekcm.so

I will do further refactorings in KCMUtils, but for now this should simplify testing of KCMs.