Mailing list mode now includes the 'no echo' option: to only receive emails of posts not created
by you. If you reply to an email thread in mailing list mode, your reply will not then be echoed
back to you in a duplicate email by the system.
* 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
Kiril Staikov
James Kiesel