Adds config options for modifying the spawn rates of Wandering Traders.
These values are all easy to understand and configure after a quick read of this
page on the Minecraft wiki: https://minecraft.wiki/wiki/Wandering_Trader#Spawning
Usages of the vanilla WanderingTraderSpawnDelay and WanderingTraderSpawnChance values
in IWorldServerData are removed as they were only used in certain places, with hardcoded
values used in other places.