5.1.0: Elo rater improvements

Elo rater

• Improved chart in shooter stats modal
  • Now shows absolute rating instead of rating delta
  • Mousing over the rating history line highlights the associated rating event in the history list
• Match score blend feature: in by-stage mode, mix in a proportion of a shooter's match score into his stage scores, to help limit the impact of bad stages
  • WIP, doesn't work very well at solving the stated issue yet
• Tremendous improvements in speed (rates all L2+ matches since 2020 in about 25 seconds)
  • There's more meat on the bone, too, but the low-hanging fruit is mostly taken car of
• Match cache loading now has a progress bar

Fixes

• Result viewer no longer lists all stage scores as 'null' when exiting what-if mode
• Result viewer retains selected stages when leaving what-if mode
• Elo rater on Linux no longer gets stuck on one tab after a short time