Make better and more types of ground scars

[GoogleFrog]

The ground scars I slapped together are growing on me, but we can surely do better.

• The tiny ground scars look a bit dark and point-like. Perhaps we should fiddle with the weapon-side alpha and fadeout parameters.
• Different explosions want different types of scar. Eg Badger feels like it wants something closer to Jugglenaut stomp than the generic scar.
• Starlight uses the generic scar and looks ok, but a bit weird. I like how it leaves a dark trail though.
• I was not able to fully solve the blurry overlap problem.