Silent Lightning API

The lightning entity, when spawned, will *always* fire a very loud (volume 10000F) sound packet that most if not all players in the world will hear.
This PR introduces a way to spawn lightning that doesn't make any sounds by adding a flag that short-circuits the sound logic for the silent strikes, for use in giving lightning quieter/different sounds, without having to edit packets.

The LightningStrike Bukkit entity is also updated with a getter the silent state.