Add a workspace selector which counts layers on the current workspace/monitor

[kamack38]

I'd like to have a layer selector (l) which would work similarly to the window selector (w). It would count the number of layers in the current workspace/monitor.

This would allow users to add top gaps for the monitor where the Waybar is. Here's an example:

workspace = l[2-99], gapsout:5 0 0 0 # Adds top gaps when there is more than one layer (Wallpaper + Waybar)