* Add database support for list show-reply preferences

* Add backend support to read and update list-specific show_replies settings

* Add basic UI to set list replies setting

* Add specs for list replies policy

* Switch "cycling" reply policy link to a set of radio inputs

* Capitalize replies_policy strings

* Change radio button design to be consistent with that of the directory explorer

* Add optimistic lock to avoid race conditions when handling votes

* Force-reload polls when getting `ActiveRecord::StaleObjectError`