More palette un-hardcoding

This time muzzle flashes and tesla zaps.

The muzzle flash customization is a bit limited because the palette is defined under WithMuzzleFlash which is no longer on a per-muzzle/weapon base, so all muzzles of a unit must use the same muzzle palette. Neither an issue for any of the mods currently shipping with OpenRA nor for the TS mod, though.
Similar situation with AttackGarrisoned, which defines only one muzzle palette.