Add local-model-only flag to joint analyses

[bfhealy]

This PR adds a local-model-only flag to joint analyses to avoid downloading models from gitlab/zenodo.

(Several automated linting updates to the code as well)

[bfhealy]

@bking-astro Once merged, this should allow you to skip the model download process by adding local-model-only=True to the ## EM arguments section of your config.ini file.

[sahiljhawar]

@bking-astro Can you test this locally and confirm if this works?

[bfhealy]

Update: the flag appears to be working as intended, but we're working through what may be a cluster-specific issue with mpi.

[sahiljhawar]

LGTM