Immersive Cavegen

- Added two new mobs:

  - Brown Cave Spiders (come in three sizes, the bigger the size, the more chance of poisoning you)

  - Glowing Slimes (slimes but they spawn underground, glow in the dark and spill water when they die)

- Fixed bug with strongholds not spawning where they are supposed to, leading to unusable eyes of ender

- Fixed bug with huge mushrooms appearing above ground

- Added integration with Immersive Snowgen, my other mod (previously, they wouldn't work together)