Track inventory pickups and drops for each level

This prevents farming of materials in levels and allows for the transport of materials from one level to another via a player inventory.

I've only tested this with materials that spawn in the levels so far and I know that it doesn't work with inventory cheats as there is no original level or position to track from which confuses things at the moment.

Have a look and toss out ideas for improvements. I don't think it makes much sense for me to continue developing this further until we've had some input on potentially better methods.