Automate path_config usage

[sweverett]

Right now on the grid-test branch, we handle the different directory & file paths between users with a small path_config that can be piped into various pipeline runners to populate the typical configs with. This works for now and is pretty painless, but we could eliminate the need for it by instead parsing all file paths w/ a new utils function that replaces some standard keyword with a utils call, e.g. MODULE_DIR/galsim/data/ could be parsed into {utils.get_module_dir()}/galsim/data automatically.

Would be handy, but not a top priority right now.