Hide panel thumbnails when current window is fullscreen
when the focused window is fullscreen, it is supposed to go on top of the panel, but not when something else is focused
we can't replicate this easily on the overview effect side as the parent hyerarchy is that all the windows are children of the wallpaper thumbnail which is sibling of the panels thumbnails so either the panel is in front of everything else or in the back.
to obviate that, hide the panel thumbnail when the current window is fullscreen
Edited by Marco Martin