MDL-32888 Grader report: added user search
MDL-32888 Grader report: refined user search
MDL-32888 Grader report: refined user search with no reset
MDL-32888 Grader report: cater for suspended students
MDL-32888 Grader report: use SESSION object and DB functions
MDL-32888 Grader report: Refined SESSION and api function use