use OCS to retrieve Tabs from the KDE store
Summary:
newstuff.kde.org has been shut down for a while and as a result the KNS
intergation was entirely broken. We've got a new System Montior Tabs
category on store.kde.org now which we can use instead.
BUG: 338669
Test Plan:
- open kns dialog
- install 'hard disk totals'
- close dialog
- find new tab for hard disk totals
Reviewers: Plasma, leinir, jriddell, apol
Reviewed By: apol
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D8734