Xeno blood rewrite + Xeno blood burns people

I am angry at:
- the coder who copy pasted blood code and used it again for xenoblood
- the coder who saw this mess and placed a snarky comment instead of fixing it.


I'm not 100% happy with how I handled adding xeno blood burning to trail_holder objects, but they're dodgy as fuck so I added another variable that will allow people to check what type the trail is, since all trail_holder objects are the same typepath regardless of being blood or xeno blood, etc.


Changes:
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- Xeno blood has changed path from /xenoblood to /blood/xeno, all subtypes of xenoblood are updated including gibs.
- Xeno blood now deals 10 burn damage to whoever walks over it.
Won't this burn aliens, too? Also that's a ton of burn to apply per splatter and aliens might try to abuse the shit out of this by having one get hit a little then pushing people on the blood.