Let user specify weights for what-if

[X] I have searched the issues and believe that it has not already been requested (and possibly rejected)
[X] I have made sure that this feature isn't possible with this project's plugin system and/or configuration and core changes must be made to make this happen
[X] I agree to follow the Code of Conduct

If the student knows the weighted grade of the assignments, let them input that

ThatXliner / skootils