restructure windows previews to plasma design

--previews showed some strange behavior by
re-introducing faulty or empty previews under
X11. Best way to approach this is to follow up
plasma design idea in order for the code to be
comparable. The code was updated and the introduced
issue shows to be fixed but this wants users
feedback.

BUG: 397193
FIXED-IN: 0.8.1
(cherry picked from commit b4a7b1ac844f2ced04f63b8c5e5d7c2d6619b7cb)