Parameterize photo-z files and revise data file download logic

[manning-ncsa]

The data file locations have been parameterized to support custom locations for the dust model files and photo-z weights file, and the download of these data files is skipped if the required files are already in place. This supports deployments where data files are provisioned upon initialization from a self-hosted data set and/or where redundant downloads are undesirable.

[alexandergagliano]

@manning-ncsa looks like the unit tests fail because with your change, the code tries to open a tarball where it finds a directory:

../../astro_ghost/photoz_helper.py:358: in load_lupton_model
    build_sfd_dir(file_path=dust_path)
../../astro_ghost/photoz_helper.py:59: in build_sfd_dir
    tar = tarfile.open(file_path)

Could you change this and update the pull request?

[manning-ncsa]

Oops. Fixed in commit b912762

[manning-ncsa]

Another stupid mistake! Can I run this locally before pushing another commit? I think these errors were hidden from me when I ran the Blast code that calls calc_photoz() because they are caught in an exception block in a print statement that is easy to miss.