Added WorldInfo mappings

Added fields and methods for net.minecraft.world.storage.WorldInfo in
mappings.conf.
Implementation of WorldInfo mappings

Added declarations to World interface and functions to GraniteWorld.
Merge branch 'SmoothGranite' of https://github.com/Chrisbotcom/Granite into Chrisbotcom-SmoothGranite

Conflicts:
	src/main/java/org/granitemc/granite/world/GraniteWorld.java
Merge branch 'Chrisbotcom-SmoothGranite'