Panel does not reserve space on screen

[thm-unix]

Bug Report

Panel does not reserve space on screen

Steps to reproduce

1. Run plainPanel
2. Maximize any window

Screenshot

[thm-unix]

According to https://specifications.freedesktop.org/wm-spec/wm-spec-1.3.html, _NET_WM_STRUT flag is responsible for reserving space on screen. We should use it.

[thm-unix]

We used KWindowSystem to create Window List applet and to set strut (KWindowSystem::setStrut). Bug is fixed.