- Totally new spawner, with a new algorithm:
  - spawn is more dynamic
  - spawn is better distributed, monsters are not anymore stacked on the borders
  of the screen
  - spawn don't depend on the "current biome" (biome where the player is located)
  but on the monster's spawn location, so if you are on the edge of two biomes,
  monsters of each biome can spawn
  - works well in multiplayer
  - spawn engine is more customizable, and will allow us to create persistant
  world bosses, or persistant monsters (that remains after a save and quit).
  It allow also a better control on the number of monster spawned per chunk,
  and their attributes (effects, levels, etc...)

Multiplayer fix:
- Pet house items points and experience gain are not sync
- Crash if a chest window is open and the player die (work also for other objects)
- Spawner don't work anymore if a client is transformed and return to
  it's normal state (detransform), and some other problems