Add block mappings

[Seggan]

Changes

Added block mappings, and made some changes to world gen

Related Issues

Checklist

• [ ] I have fully tested the proposed changes and promise that they will not break world generation, mob spawning, and the like.
• [x] I followed the existing code standards and didn't mess up the formatting.
• [ ] I did my best to add documentation to any public classes or methods I added.
• [x] I have added Nonnull and Nullable annotations to my methods to indicate their behaviour for null values