Track assignee for issue (#808)

* track assignee for issue

* fix lint

* use getUserByID instead Get

options/locale/locale_en-US.ini

@@ -546,6 +546,9 @@ issues.remove_label_at = `removed the <div class="ui label" style="color: %s; ba
 issues.add_milestone_at = `added this to the <b>%s</b> milestone %s`
 issues.change_milestone_at = `modified the milestone from <b>%s</b> to <b>%s</b> %s`
 issues.remove_milestone_at = `removed this from the <b>%s</b> milestone %s`
+issues.self_assign_at = `self-assigned this %s`
+issues.add_assignee_at = `was assigned by <b>%s</b> %s`
+issues.remove_assignee_at = `removed their assignment %s`
 issues.open_tab = %d Open
 issues.close_tab = %d Closed
 issues.filter_label = Label