Overhauled chunk layers to be agnostic of their overworld/dungeon status.
There are still some things that need to be decoupled from chunk layers. Ideally
they should just be a data model with some accessors. At deserialization,
spawners get placed at (25,25). This is temporary; I will change it along with
some overhaul of the spawner/stair creation/management systems.
Merge branch 'master' of https://github.com/schiem/roguelike into chunk-overworld-merge

Conflicts:
	src/gui/game.h
Trying to merge.
Merge branch 'chunk-overworld-merge' of https://github.com/schiem/roguelike