Add layer support

[Pysis868]

Not sure what or how exactly. Danilos mentioned it and can probably work on it more.

When I hear the vague description, it seems like further map entries, rather than additional layers, but I am unfamiliar how necessary it is for the new TotK game. I keep comparing it to what I heard and know of the Light and Dark worlds from SNES ALttP.

The key thought is the end result being different images to show, so not a big problem which choice for now.
But also, see if any markers and other objects need an additional index, not just by map, but in combination by layer as well.