Partially fix #112: Record email addresses from CFF

[sdruskat]

This PR is a partial fix for #112, in that it uses the branch for this PR against cffconvert to record email addresses in CFF files.

Review checklist

• Run

git fetch origin
git switch feature/record-cff-email
git pull
poetry shell
poetry install
pytest test/

... and all tests should pass.

• Review changed files manually
• Run HERMES against this local repo and check in the .hermes files if emails made it over from CFF.

[led02]

chore: Just some minor cosmetics...

[led02]

praise: Works for me (almost)