* Redesign message notification emails. * Fix tests and linter. * Fix tests * Fix tests * gofmt. * Fix date separator * Update html files * Remove date for message notification email. * Modify subtitle for mentions and direct and group messages. * Fix lint error * Fix DM subtitle. * Fixing translations Co-authored-by: Mattermod <mattermod@users.noreply.github.com> Co-authored-by: Jesús Espino <jespinog@gmail.com>