Adds water piff(s) animations to machine gun/pistol/rifle weapons.
Adds explosion sequences for flak.shp and veh-hit1.shp, labeled small_explosion_air and med_explosion_air, respectively.
Changes Explosion from med_explosion to either small_explosion_air or med_explosion_air for several weapons that are (mostly) anti-air, for more animation variety.
Changes explosion animations for artillery, cruiser and missile sub weapons from large_explosion to artillery_explosion.
WaterImpactSound overhaul.
Nearly all ballistic or missile weapons now have a splash sound when hitting water.
ImpactSound overhaul.
Nearly all cannons and missiles now have ImpactSounds. Rule of thumb: kaboom12 for cannons (tanks, gun turret), kaboom15 for artillery weapons (cruiser, missile sub, artillery), kaboom25 for missiles.
Exceptions are the Flak Truck and Light Tank, due to their high rate of fire.
Merge pull request #3651 from reaperrr/ra-explosions

RA mod Explosion & ImpactSound revamp