Floating Island World Generation

Minor changes:

• Fixed biome setter to set the biome if no parent worldgen is set
  
• Pigman spawners on nether islands now spawn when a player is within 64 blocks
  
• Spawners in dungeons now spawn when a player is within 26 blocks
  
• There should no longer be warnings in the console about spawners when an island generates over another island
  
• Tiny performance increase involving spawners
  
• Gravel no longer replaces bottom blocks on islands, to prevent lag if this happens on desert islands and the gravel falls

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. Known issues:
Fjord trees occasionally generate on the islands.
Server crashes when using 173generator (not sure if up to date).