Enter grades for past courses

[noabarlia]

As a user, I would like to be able to enter grades for my past courses, and perhaps see some statistics (total average, average per year, etc.).
I think this will be very helpful, as for some students grades are a major consideration when planning a degree.
From a privacy standpoint, some users may not want to disclose this information, so my suggestion is to make this feature optional (perhaps adding a checkbox on the user definition page).

[nmdanny]

This somewhat a duplicate of #77 - though I proposed using the course statistics, and not the individual User's grades, which would probably be better from a privacy standpoint.

However, using the individual User's grades might provide better analytical insights(e.g, knowing that a student who takes courses X and Y in the same semester tends to have lower grades than the averages in those courses, might hint it's a bad idea to take both of them in the same semester)