* Add trending links
* Add overriding specific links trendability
* Add link type to preview cards and only trend articles
Change trends review notifications from being sent every 5 minutes to being sent every 2 hours
Change threshold from 5 unique accounts to 15 unique accounts
* Fix tests
* Fix language filter codes
CLD3 returns BCP-47 language identifier, filter settings expect
identifiers in the ISO 639-1 format. Convert between formats,
and exclude duplicate languages from filter choices (zh-CN->zh)
* Fix zh name
* Add failing spec showing that human_locales does not match what i18n knows about
* Add missing `ar` key for arabic to human locales
* Remove duplicate `id` key from available locales
* Sort keys in human locales list
* Add spec for human_locale helper
Matt Jankowski