KCM KWinTabBox manage KCModule states

Summary:
Following D27323, manage KCModule states for reinitialize/defaults/apply

Also, this should solve :

BUG: 414567
BUG: 387160
FIXED-IN: 5.19

Reviewers: #kwin, ervin, bport, meven, zzag

Reviewed By: #kwin, ervin, meven, zzag

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D27784