Update to the new way to layout window overlays, which requires
setting a slot on the clone, and update to the new padding setting
for the window picker, including a custom style to avoid placing titles
outside the clip area.
3.7 is brought some big changes in the window layout code, but I'm not
going to take advantage of them (as the assume some sort of row based layout).
Instead, just work around them in a way that makes the extension work
without major issues.
This extension employs an algorithm (taken from KDE) for layouting
the thumbnails in the overview that more closely reflects the positions
and relative sizes of the actual windows, instead of using a fixed
grid.
