Fixed many slime bugs.

- Fixed slime hurt/death sound
- Added slime spawning on death
- Fixed the max health
- Fixed the attack damage
- Little slimes should not attack players (fixes #1202)
If so, then [this](https://github.com/mc-server/MCServer/pull/1205/files#diff-3193dc6b784abe5edaf2c1f2cf3646a2R12) comment is wrong, at the very least.