Store particles and entities in Bevy's world

[eira-fransham]

Motivation

See #1

Proposal

We eventually want to migrate all client behaviour into Bevy systems, but doing so is a huge amount of work. The smallest possible first step would be to remove the vector of entities/particles from the ClientState struct itself, and store those objects in the bevy::World. The behaviour would still be in the same methods on ClientState, but the methods would take Querys as parameters instead of storing that data in fields

Issues

We still pass the entire ClientState to the render thread, so we need to make sure that the correct data is still being passed now that it lives in components. Ideally, we would use regular Bevy types like Transform if we need the origin.