Changes

The whole cargo generator was dramatically changed since previous versions.:

Main changes: * # Cargo is now defined by units instead of simple weight. One unit of cargo takes some volume, which gives count of unit that might fit into trailer body. From this unit count mass and reward are also derived. Mass is subject for further limitation either by trailer itself or country laws. Both might result in decreasing of cargo unit count loaded.* # Another new concept are body types, trailers and cargo are not linked directly but rather they are being matched by body types. Trailer that has body type '''flatbed''' will have only generated jobs that consists of cargo that is compatible with '''flatbed''' body.