Consolidate `--where-project` and `--project-name` in `babs-init`

[tsalo]

Summary

I think we could just have a --project-root parameter or a single positional argument (see #172).

Additional details

Simpler command-line interface.

[tsalo]

Just to provide more context- --where-project is the directory in which a new folder (--project-name) will be created. It seems easier to just do --project-root or a positional argument that points to a folder that doesn't exist.