Floating Island World Generation

Minor changes:

• Ores no longer generate in sand (custom ores still can)
  
• Desert islands are now mostly sandstone instead of mostly sand
  
• Fixed nether ores being placed mid-air at lake islands

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).