Add supply teachers in teachers class list

orm/class.go

@@ -13,7 +13,7 @@ var (
 
 	selectUniqueClassTeachers = `
 SELECT teachers.* FROM activities
-INNER JOIN teachers on teachers.id=activities.teacher_id
+INNER JOIN teachers on (teachers.id=activities.teacher_id OR teachers.id=activities.supply_teacher_id)
 WHERE class_id=?
 `
 )