Floating Island World Generation

Minor Changes:

• New island type: None (doesn't spawn an island for that slot)
  
• An unlinked dungeon can now spawn on an island that allows a linked one, but that doesn't have a linked one
  
• Split config option for dungeon chance into 2 separate chances for both types, old config value is respected during conversion and becomes the new dungeonchance.linked one

Using a parent generator is subject to bugs out of my control, such as the parent generator affecting the placed islands or crashes because of incompatibility.
Using large island sizes may cause bugs such as chunks not loading for clients.

Flowing water blocks spawn in 'space' for seemingly no reason.
The biome in 'space' isn't being set and instead retains the vanilla biome map.