[Permission] Limiting gradebook access for TA/Grader roles

[abbyrosensweig]

We'd like instructors to have the ability to turn off gradebook access to people of certain roles in a course. Alternately, we'd like to be able to turn off gradebook access within a custom role.

The use case here is that there are times when graders should be able to grade specific assignments but they should not be able to view the full gradebook. For example, if undergraduate graders are assigned to a course and will be completing grading on certain assignments (like homework), they should not be able to view the full gradebook as this creates a security risk. Grading permissions currently allow viewing of the gradebook. We'd like to be able to control/limit that gradebook access.