Add better thunder effect

This PR adds sounds to thunder and better randoms in lightning.
@turt2live Because it's not the same: SendWeather send the StateChangeMessage packet once with a value of 1 or 2 to stop or start raining.

During a transition, the rain density and sky darkness changes smoothly with a step of 0.01F on each tick: in this case the StateChangeMessage packet is sent more frequently but weather doesn't change (start/stop raining).