Add grade students group permission

I had to make two additional changes to get this to work on my local sandbox:

1. Updated the students view to use 'grade students' instead of 'edit group' for the group permission.

2. The 'results' access op was also still using the 'edit group' permission, needed to change this to 'grade students' too otherwise the results page itself was not accessible

With both of those changes, a course member with the 'facilitator' role and a couple of permissions was able to grade a student.

This is merged. I'd appreciate some additional manual testing before tagging a new release since in my own testing I found one outstanding issue and had to make a couple of configuration changes in order to be able to use it.

Automatically closed - issue fixed for 2 weeks with no activity.