Hydro cargo points

Mainly this allows mutant seeds to be sold to CentComm for cargo points.  The bounty for discovering a species is the seed's "rarity", which ranges from 10-50.  Only mutant seeds and slime/admin only seeds have rarity values.  If a more potent sample of the unusual seed is sent, more points are awarded (1 point for each point of potency).

Also, the "species" property of grown items wasn't being set by slimes and the spawn command.  It was essentially unused so I removed it to resolve the issue.