Added ExplosionPalette and WaterExplosionPalette traits to Warheads.

This is needed for TS water splashes, for example (they use unit*.pal instead of anim.pal).
Defaults to "effect".
Merge pull request #5125 from reaperrr/explosion-palette

Added ExplosionPalette and WaterExplosionPalette traits to Warheads