Please restore email digests

[joebuhlig]

Here you go! I wrapped this up late last week and we let it run with no issues over the weekend.

Restore Mailing List Mode Daily Summary

For a variety of reasons the option for mailing list mode users to receive a daily summary email was removed. It turns out there are a handful of communities that relied on this feature and as such it provoked a good discussion about the restoration of the feature. It was mentioned in that topic that I was working on this. Thanks to @lkramer and team for sponsoring this work! This plugin adds an option to the email preferences for a user and allows them to enable the daily emails. It i…