Improving races with more and varied opponents

This update covers a lot of quality of life improvements, with better and more varied artificial intelligence, improved physics, several bug fixes and a first preview of crash animations and sounds.

Update notes for version 20201208

• Increased number of AI racers from 4 to 6
• Improved differences and spread between AIs
• Optimized performance for split-screen multiplayer in HTML5 version
• Improved crash physics
• Introduced animations and sounds for crashes between player and AI
• Corrected AI bug in Catalunya
• Corrected bug where cups' second races always showed 1st placed
• Optimized performance for cars' particle emitters
• Fixed bug where tires and particles showed above Player 2's car in HTML5 version 
• Fixed critical bug where game would hang if Player was steering before the race started

I am hunting down a nasty bug where the game is unresponsive on its first load in Chrome. It only happens when I post a new build. If you experience it, you can change to another tab and return or reload the page, that should make the game work again. I hope to have it identified and squashed for the next build.