Fix for a bunch of Tropicraft stuff

[LordEpos]

Low Priority.
https://www.curseforge.com/minecraft/mc-mods/tropicraft
Three different issues I've stumbled upon with the latest 1.12.x build of this one:

• The Koa Villager mobs cause a crash very regularly when wandering around the world which makes it impossible to re-enter the world without instantly crashing again. Either fixing the crash or an option to prevent the villagers/villages from spawning would fix the issue.
• All mobs using the Multimob library spawn in the tropics, regardless of their normal spawn rules. This includes the Multimob Core Dummy, a white rectangle that does nothing.
• The config options to spawn mobs from Tropicraft in the Overworld do not work.