Implement several more world methods

I have tested all of these methods except `getBiome` and `setSeed`

I'm not sure about the `getBiome` method and so it could be removed if it's not going to work

There are some comments which it'd be good to have some input on
There is a better way to do this, WorldServer holds a Map of 'entitiesByUuid' which you can use to directly lookup the entity.