Restructure how creatures and inventories are being stored.

This will allow iterating through the creatures on the map without
needing to iterate over every single tile.  Also creatures all have
their own inventories, so it may be possible to display multiple
creatures per tile.
Fix ui crash.
why was this even here?
Equipped item material specification.
Rename AddBuilding and AddCreature to PushBuilding and PushCreature.
Fixed incorrect vector use.

Version is now stable.