Change ELO system to use TrueSkill

[Ooglely]

Title self-explanatory. TrueSkill is a much better way to have a skill rating for a project like this because it is designed for team-based games, while taking the average ELO of a team and applying the same change effect to each of them doesn't necessarily produce consistent results.

Some links to reference:
https://www.microsoft.com/en-us/research/wp-content/uploads/2007/01/NIPS2006_0688.pdf
https://www.moserware.com/assets/computing-your-skill/The%20Math%20Behind%20TrueSkill.pdf

There exists a python package that already implements it that could be used: https://trueskill.org/

[Ooglely]

Specific passtime stats can be retrieved from passtime logs thanks to https://github.com/blakeplusplus/p4sstime, can use for elo calculations in the overhaul