[WIP] Support for item weight and volume, storage space

**Do not merge this yet!**

Making a PR for this so that I can talk about it and possibly bounce ideas around, and make notes of certain things for when I come back to work on it later.

One particular thing I should note immediately.. some integers are becoming floats when I really don't want them being integers in the first place.  I need to fix that because it's gimping the player's max storage space.