High quality emitters need to maintain state themselves. For example, this it needs to remember when it spawned the last particle. This is especially important when the birth rate is changing over time. Otherwise, there will be very visible artifacts. It is quite likely that other components of the simulation need their own state as well. Therefore, I refactored the `SimulationState` type a bit, to make it more extensible. Instead of using hardcoded type numbers, a string is used to identify the state type. Also, instead of having switch statements in many places, there is a new `SimulationStateType` that encapsulates information about how a specific state is created/freed/copied/... I removed the integration with the point cache for now, because it was not used anyway in it's current state.