Define the desirements for the grade history report

The primary goal of integrating the Grade History report is covered in MDL-46191 and it's sub-tasks. Stage 2 of this will be the potential enhancement of the report.

This issue is a placeholder that will act as a collecting point for extensions to the existing report after it has been introduced. Ideas should be well described and documented in order for mockups, specs, and code development to happen.

The following ideas have already been suggested.

• Diffs (showing differences between two points in time)
• Finding editing periods (what does this mean?)
• Include grade history in backups
• Restore grade history from backups
• more ideas from you...

Once ideas have been defined and speced, improvement issues will need to be created.