`workspaces()` doesn't include windows in the scratchpad which means
they're left transparent when the script exits. This just iterates over
the scratchpad containers as well and resets their opacity.
Transparency gets reset when the script is terminated.
Added command line option to set transparency strength without changing
the script.
Added support for multiple displays.
Sway has ability to apply transparency to arbitrary windows. This script
wires up this functional to one of popular use-cases from
i3+<compositor_name>.
Signed-off-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
