Added a sound variant for light planes.

Added more naval sounds and tweaked some existing sounds.

Forgot about the scout planes, added sounds to them now. Might add country variants in the future but for now they all share the same sound.

Added sounds for plane bombing and shot down sfx, mechanized and mg tank firing, infantry artillery firing and nuke explosion.

Added sounds to some of the rocket artillery units.

Added cannon sounds to ships.

Added tank cannon sounds.

Added infantry machine gun sounds.

Added infantry rifle firing and bolt sounds. May tweak a few of them in the future.

Added plane gunfire sounds. May change them later.