Add total_grade to grade_entry_students
Add total_grade to grade_entry_students
Updated calculating grade entry form marks and average

Moved calculate_total_mark(student_id) from grade_entry_form to
grade_entry_student and renamed to update_total_grade.

The total gets updated after every grade update.

The average gets calculated every time the student dashboard loads but
now just gets each student's total grade instead of looking at each
grade for each student.
Only save total_grade if it has changed
Changed calculate_total_percent to take a grade_entry_student and methods update total if nil
Update grade now supports deleting grades
Updated unit tests