Workspace KCM Redesign Using Kirigami

Summary:
Workspace KCM is redesigned by using Kirigami. Functionality is same. Recommendations are welcome.

New design:
{F5856982}

Old design:
{F5861690}

Reviewers: ngraham, romangg, #plasma

Reviewed By: ngraham

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D12973