Z-level split.

Splits each individual Z-level into its own map file.

**Pros**
* Work on different Z-levels will no longer cause merge conflicts.
* Git history size will not grow as rapidly as only individual Z-level files are saved, instead of the entire map.
* Somehow the total map-size went from 3.2MB to 2.86MB. Expected the opposite but the maps do look fine. Did expect to list this as a con but I won't complain.

**Cons**
* Map changes on master will for all practical purposes be lost until the split is merged into the branch.