KCM KWinScreenEdges port to KConfigXT
Summary: Following D27862 port KWinScreenEdges to KConfigXT, handle isSaveNeeded and isDefault KCModule state.
Reviewers: KWin, ervin, bport, meven, zzag
Reviewed By: KWin, ervin, zzag
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D28475