PublicationEmail to be more configurable, to load preferences

[gnott]

A simple modification in PR #681 satisfies the immediate request to not email authors when a retraction is published.

Other journals may have different article types, or want to email authors when all articles are published.

To make the activity more configurable, the list of "do not send" article types, as well as the email template names to use for each type of article can be moved to a preferences file. In this way, the value are not in the activity code itself.

The preferences file could by a YAML or configuration file, to be determined.

[gnott]

This may be a good issue to review @fred-atherden, including how to make preprint email sending.

[fred-atherden]

Thanks G - good point. I'm not sure what we're not sending for right now, but I'd be interested to know.

I'd think we'd like to exclude editorial, correction, and retraction. I don't think there are any changes related to reviewed preprints to consider here, but in the event anything changes it would be good to reconsider whether this needs changing.

I like the idea of having a configuration file or similar to document the preferences.