Added the possibility for paratroopers to die on impact

as proposed in #5493. `LandOnlyInSuitableCell = false` is useful for testing purposes, but may be annoying for the players loosing their careless paratroopers so I made this an option we can simply disable later.
You still haven't fixed this: you just changed "shadow on head" to "shadow on feet".  This needs to be drawn on the ground (`pos - new WVec(0, 0, pos.Z)`).