Further AI balancing

[freeman2344]

The AIs currently tend to build fairly crappy vehicles. While their general behavior has somewhat improved with recent changes, the design side of things still needs some refinement.

1. The AI needs to design more competitive and realistic components, especially engines (AIs with 700cc engines in 1990 are not a rare occurrence).

2. The AI needs to design vehicles with higher ratings in general.

[Tridon]

This could be dependant on the difficulty setting perhaps. On easy the AI will make quite a few wonky and suboptimal cars, while at hard the cars will have higher ratings and fit the market much better.

[freeman2344]

Interesting, I'll try hard later today.