pre-flattening

This MR adds pre flattening support (#26 (closed)).

It contains a lot of fixes and code changes.

Tasks:

• properly integrate pack_format (settings per connection) => independent protocol version and assets fix val packFormat = context.connection.assetsManager.properties?.pack?.format ?: if(context.connection.version.flattened) Int.MAX_VALUE else 0 // TODO: integrate with assets/refactor_atlas
• registry tests
• custom block model tests (e.g. SnowyBlock)
• translations broken (key changed)
• store translationKey in blocks.json and items.json

And fix up block models:

• sponge and wet_sponge -> sponge[wet=true], sponge[wet=false]
• grass, mycelium (snowy)
• multiparts
  • fences
  • walls
  • redstone
  • fire
  • glass panes
  • stairs
• doors
• beds (>1.12, block entity determinate the color)
• flowers, flower pot (determinate the flower)
• note block (just for interacting)
• repeater (powered)
• oak log/oak wood [axis=none]
• trip wire?
• slabs (double)
• furnace? (lit=true/false)
• rails
• anvil damage

Closes #112 (closed)