Port to < 1.13 (17w47a)

17w47a was the "flattening update". Before this, all ids where more or less hardcoded. There are 2 main problems with this:

• No deobfuscation mappings for this version (We could use MCP, but... uff.)
  • Yarn mappings should exist for 1.12, but needs testing
• Port PixLyzer with meta data. How exactly is it stored, etc?

The current yarn port just works until somewhat 1.14. See #2 for progress for 1.13.