Cargo should be sold (or discarded) when buying a new ship

[cjstokols]

When you buy a new ship, all cargo should be sold. However, if a certain trade good cannot be sold on that planet, it is lost with no compsensation. (So the player should try and sell all their goods before selling a ship)

[cjstokols]

The player should be notified that their cargo and equipment is being sold, (or discarded) before they finalize their purchase.