08: Check for empty/malformed chapters, authors

[hlieberman]

This check replaces what is currently known as steps G (invalid author names), I (invalid author email addresses), and J (empty chapters). Note, it does not confirm that email addresses are in any way valid, or even properly formatted; merely that the import of whatever is in the column won't break the archive.

[ariana-paris]

I wonder if in future, we might want to have all the checks run in one go and produce a report that the operator can slog through to pick off issues in random order, rather than stalling them on one issue at a time in a fixed order. They could also do with some automated testing to make sure nobody breaks them in future. But this is already so much better than relying on manual checks! 🏅