[Gradebook] Separate permission for posting grades apart from editing grades

[stelpstra]

Currently the permission for editing grades gives graders the right to also post grades. This means that different tutors (per section or group) can post grades earlier than others. It should be possible to prevent this, better the teacher / course coordinator etc. should have this permission.

We considered Moderated Grading, but it adds more complexity to the process and it is limited not supporting up to 10 tutors or more. Also, moderated grading should be improved first, e.g. with:

• https://community.canvaslms.com/ideas/16308-moderated-grading-improvements 
• https://community.canvaslms.com/ideas/16412-moderated-grading-improvements-2 

So moderated grading is not a suitable workaround.

Please separate permission for posting grades apart from editing grades.