* Rearrange frontend to account for mailing list mode
* Allow update of user preference for mailing list frequency
* Add mailing list frequency estimate
* Simplify frequency estimate; disable activity summary for mailing list mode
* Remove combined updates
* Add specs for enqueue mailing list mode job
* Write mailing list method for mailer
* Fix linting error
* Account for stale topics
* Add translations for default mailing list setting
* One query for mailing list topics
* Fix failing spec
* WIP
* Flesh out html template
* First pass at text-based mailing list summary
* Add user avatar
* Properly format posts for mailing list
* Move make_all_links_absolute into Email::Styles
* Apply first_seen_at to user
* Send mailing list email summary hourly based on first_seen_at
* Branch and test cleanup
* Use existing mailing list mode estimate
* Fix failing specs
