[Gradebook] Export individual grades as percentages

[MikeDombroski]

Problem statement:

In Grades, current individual assignments cannot be exported as percentages, only raw scores. Grades for individual assignments can be displayed as percentages, but won't export as percentages.

Proposed solution:

Allow the option for instructors to export individual assignment grades as percentages as well as raw scores. This will allow instructors to have a csv file with percentages.

User role(s):

admin,instructor,ta,designer