Adjusts train supply costs to make the tug/cart ratio choice more interesting for players.

Lowering the cost of carts gives players the option of making a tradeoff between less cost per cargo slots vs greater overall speed. This is because a train with less engines and more carts will be slower, but will cost less per cargo space.

Raised the cost of a tug so that the standard 1-tug 3-cart train costs 90 points as it did before.