Ground scars for fire

[GoogleFrog]

The new ground scar system lets us have per-weapon scars. Fire-based weapons could gain scars using this. Currently, many fire weapons lack scars or have tiny scar radius because their base damage is too low to be detected as a scar weapon by the engine. The scar could have some sort of burn effect, and probably wants to be subtle, especially for large AoE weapons such as Inferno.

Related: #5406