Sway provides the workspace "num" property which is an integer number of
the workspace, i.e., workspace "3" -> 3 and also "3dev" -> "3". This
commit uses this property to sort the workspaces, which makes sense when
persistent workspaces or all-output is specified. This commit also adds
a new configuration option, whether the numeric workspaces come in front
or after workspaces that have non-numeric name.
All workspace buttons that are visible on the same output as the current waybar can be styled with the `current_output` css class.
This is really only useful in combination with the `"all-outputs":
true`. Then the workspaces that are on the current output can be styled
differently than the workspace on other outputs, while all are visible
in the waybar.
Michael Rodler