[Gradebook] Allow Grading Period overrides to be calculated into Final Grade

[joni]

Currently, when using Multiple Grading Periods, you can override a student's grade for each individual grading period in a course. This is a great feature we use a lot - however, when running reports, the overridden grade does not calculate into the final grade. We would have to manually override the final grade again at the end of the term after already overriding each grading period. 

Please allow an option at the admin level to have the override grade actually be used in final grade calculations.