add just-i18n package
i18n - add korean language
set user language (profile.lang)
send email notification to assignees and reviews.
email notification when new work item body has @username mention.
merge eskim/i18n

* i18n:
  set user language (profile.lang)
  i18n - add korean language
  add just-i18n package
merge eskim/email_enhancement

* email_enhancement:
  email notification when new work item body has @username mention.
  send email notification to assignees and reviews.