Add options for forced car missions

[nmize1]

forced_cars:
Choose whether to lock forced car missions until their car is unlocked, allow you to complete the mission without unlocking the car as in vanilla, or remove forced cars and allow the missions to be done in any car.
locked: 50
vanilla: 0
remove: 0

Closely related also,

extra mission required cars:
Add required cars to more missions
true: 50
false: 0

extra required car percent:
Percent of missions to add required car to
100: 0
50: 50
10: 0

mission required cars:
Change cars required by missions
Shuffled: 50
Default: 0
Removed: 0

[nmize1]

Added more required cars options

[nmize1]

Implemented random mission locked behind cars, probably not gonna do the rest for now.