Simplify LevelLoader, place error message when level fails to load.
Set World size on constructor.
World has direct CollisionManager, add ikdtree for rooms.
Insert world's rooms into the tree.
Migrate objects rendering to the room's responsibility.
Removed layers from World.
Remove content_node from world, add camera geometry.
LevelLoader creates CollisionClasses, refactor LeveLManager singleton.
Room supports removing objects and adding objects directly.
WorldObjects change their room dynamically.