fakedata issue with test user rating deltas - generate them via cumulative sum instead

Here's what it looks like in production (which is correct)

my skill went from 22.13 to 23.0 which is a gain of 0.87

But in my dev environment (wrong deltas; ignore the lack of icons which is due to my fontawesome)

My skill went from 26.29 to 25.13 which is loss of 1.16 but it shows a gain of 1.18

The deltas are also wrong for both skill, uncertainty, and leaderboard rating. I noticed this bug when I was checking Exeler's last PR to add uncertainty to this page. But then I went back to an older state of master and this bug is still there; so the bug is not from his commit. Something wrong with fake data creation perhaps?