Various changes

Modified internal schematic to allow tile entities
Added function to add/remove tile entities to/from the world
Made main get/set block functions public for schematic class
Fixed biome setter to set the biome if no parent worldgen is set
Modified spawner placement to be more efficient and customisable
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