Check for disposable email domains

[MatzeKitt]

There is an interesting project for disposable email domains: https://github.com/disposable-email-domains/disposable-email-domains

As an alternative to #543, we could include this list (and update it regularly) locally on server-side and check comments for these email domains.

[Zodiac1978]

In some cases disposable email domains could be wanted/allowed, so this would be a breaking change. This could be an option.