Suggestion: --recursive for modules

[Spatenheinz]

I think a --recursive flag could be useful in a couple of different commands e.g. instead of --list-submodules or in --groups to also include groups from modules.

[casey]

I think --recursive is a much better name for the flag than --list-submodules. I would do this in two steps, first make --list-submodules work with --groups to display groups in submodules, and then change the name of --list-submodules to --recursive, and make --list-submodules an alias of --recursive, so that it doesn't break existing use.