Weapons FR: Flag to play child launch sound on spawn

The idea of a 'spawn sound' to play on every spawn event has been discussed with constant spawn being in place, and that's still a good idea, but equally useful for constant spawners would be to play the fire/launch sound of the child on spawn. Presumably only once, in the case of multiple simultaneous spawns. This would let you take advantage of the launch sounds of the children if you are mixing multiple spawn types on weapons