Fixes level order

[NataKilar]

Description of changes

Adjusts the level ordering code so that mapped levels are offset in case that world.maxz is greater than the minimum mapped z-index in the database. This solves an issue that was occurring with templates that are spawned pre-load (like the supply shuttle) getting overridden. Also makes it so that levels are always spawned with the correct level data, since the game doesn't like having duplicates of the Kleibkhar level datas, since they have a static ID.

[PsyCommando]

I guess this will do for now. But assigning z-levels will have to be revisited at one point. It's not reliable across saves to refer directly to z-indices instead of zlevel ids. Especially if anything z-level ordering related changes.
We'll need a way to store z-stacks and z-ids in the db. I've been investigating a few ways, but I might need to introduce the concept of z-stacks and like a "world_location" encompassing horizontally and vertically linked z-levels upstream.