Optionally, delay the visual appearance of fly pie for quick activation

[Schneegans]

Discussed in #126

^{Originally posted by Leleat September 25, 2021}
I'd like to use fly-pie in a pretty basic way (only for window management) and only go 1 layer deep. So I think having an option to delay the visual appearance of fly pie (similiar to how GNOME's altTab delays its appearance) would be good since with just 1 layer I know where all the options are and that brief flashing of the fly pie is more disruptive than helpful.