Add Muscle Cars

[ZAX25]

https://www.nfssa.com/thread-5023.html

Accepted / planned in future:
- Advanced Crew-system
- Diamond Hunt
- Free-cam mode
- Freerun on racing maps (not sure)
- Knock-Out races
- Muscle Cars (in progress)
- Dynamic Weather (not sure)
- Advanced race rooms
- New events and meetups
- New tuning parts (in progress)
- Colorable decals
- Custom License Plates
- Challenge Series
- Single decals on windows
- Hide other cars during races
- Speedtrap cameras in freerun (not sure)