Add configuration for grade scale

[Huy-Ngo]

Currently the grade is very ambiguous. Is 10 a perfect grade or barely passing? What if someone gives a 9 to a 4-scale GPA?

We therefore need a configuration for this. The supervisors and the jury cannot give a grade higher than maximum (or lower than minimum, though I assume the minimum is often 0). Additionally, there can be minimum fraction (for most cases, 0.1, 0.25, or 0.5) configuration too, so the supervisor can't give some grade like 3.1415926.

There can be a configuration for passing grade too.

There are also letter-based scale (A, B, C, D, F), but I suppose they can modify to enum it.