Polybar's config format is a bit strange, and lists in particular are
annoying to handle. This enables using normal nix lists and nested
attrsets instead.
This change is not backwards-compatible, because the INI converter
converts lists of strings to space-separated values, and this does
something else. I expect that this is only relevant for the
`modules-left` etc bar setting, but that's enough to break things :(.
da92360208