Adds new 4-door Hatchback vehicle.

[martin509]

Summary

SUMMARY: Content "Adds new 4-door hatchback car"

Purpose of change

Being a bit of a car nut, I was slightly bothered by the fact that the car called a 'Hatchback' in game, car_mini, most closely resembles a 2-seat city car such as a Smart Fortwo, and not a larger 4-door hatchback that is usually associated with the term. This PR renames the old 2-seat Hatchback to 'City Car' and introduces a 4-door variant in its place.

Describe the solution

Adds a new car, car_hatch, a small 4 door hatchback that is essentially just car_mini extended to have an extra row of seats, with storage space being hatches instead of a trunk like on a normal car. car_hatch has a fuel capacity of 40L, a midpoint between the 20L of car_mini and the 60L of car, and roughly analogous to a real-life subcompact hatchback.
car_mini is renamed from 'Hatchback' to 'City Car'.

Spawning behavior of car_hatch and car_mini is as follows: car_hatch is roughly half as common as car, except for on highways where it's 1/3 as common. car_mini's spawn density is cut in half and is now a bit less common than the Beetle, to reflect the relative rarity of city cars in most of the US. I'm not 100% familiar with how these spawn rates are balanced, so feel free to suggest changes to this.

Testing

Loaded a large city map and verified that it spawned and had all the correct parts.

Additional context