No entities were lost in this bug, just we were triggering the add entities
before they were loaded due to an inconsistent order of putting chunk into chunkmap.
Any entity that appeared to be gone on the last build will now be back.
1.13 undesirably changed behavior here that chunk load event fired
before the entities were added to the world.
This means any plugin that spawns entities in chunk load event
causes the entities to be registered to the chunk, and then
added to the world twice.
Moves Entity Add to World to be done anytime a chunk is
registered to the Chunk Map, and ignore other calls.
Fixes#1288