NPC cargo handling

[JensAyton]

NPC ships’ cargo is defined by a number of internal state flags, and actual cargo may be determined on the fly in when ejecting cargo pods. Currently, the generation is closely coupled to the ejection mechanism. This means that JS properties such as cargoSpaceUsed and cargoSpaceAvailable can’t be implemented reliably.

For 2.0, it is desirable to determine at minimum the amount of cargo and preferably its composition either when the ship is spawned, or lazily in a decoupled fashion (although I doubt there will be much advantage to that).