public ActionResult DetailsGroup(int?id)
        {
            if (id == null)
            {
                return(HttpNotFound());
            }
            Group group = groupManager.GetGroupByID(id.Value);

            if (group == null)
            {
                return(HttpNotFound());
            }
            GroupSubjects subject = new GroupSubjects();

            subject.Id       = id.Value;
            subject.Name     = group.Name;
            subject.Subjects = groupsubjManager.GetSubjectsByGroupID(id.Value);

            return(View(subject));
        }