Added ExplosionPalette and WaterExplosionPalette traits to Warheads

This is needed for TS water splashes, for example (they use unit*.pal instead of anim.pal, converting them to anim.pal results in significant quality regression due to lack of compatible colors in anim.pal).

Defaults to "effect".

Currently there aren't any test cases in the shipping mods, but I tested this with custom versions of the RA and TS mods and it worked as intended.