csopenrankings: display mean instead of sum

My first gut reaction to the "total" column was that there's no way it made any sense because it seemed very biased towards well-rounded universities (universities that are very competitive across all categories). Then I realized that the sum was equivalent to taking the mean across the 4 categories, so it does make sense.

Perhaps using the mean (rounded to 3 SF or 1 DP) would make more intuitive sense? That also allows users to understand something by looking at only a single university, e.g. "Brown's average rank is 30.3" makes sense by itself, whereas I don't think "Brown's total rank is 121" does.

If you decide to do this, it may make sense to revisit #192. You could write "Average" with a tooltip explaining that you use the geometric mean

Start by locating the csopenrankings ranking display and reviewing issue #192, since no file or test is named. Confirm whether the intended change is the mean, its rounding, and a tooltip before editing; done means the chosen value is displayed consistently and the related ranking behavior is checked.

Written by the indexing model from the issue text.