Re-enables infections, implements a wound infection system, improves body temperatures

This PR re-enables incrementing germ_level for carbon mobs, which was previously commented out. This meant that mobs never had germ_levels above 0, so it seems you could actually do surgery without washing your hands, as you would never have any germs to transfer.

This also builds on the partially-implemented wound infection system. Untreated wounds can very slowly become infected. Moving around makes it happen a bit faster. The rates might need more tweaking. I was kind of afraid to make infection happen too fast - so in it's present state the system might happen too slowly for anyone to notice.

UPDATE:
Having an infection will increase your body temperature, and body scanners now detect infections.

I also went through and reworked part of the body temperature system for humans. In particular, the effect the environment air temperature has on your body temperature is not properly dependent on the density of the air, so near-vacuum won't heat or cool you as it should. 

The normal body temperature used for body temperature regulation is now based on species, and I fixed the body temperature damage levels not being based on the species cold and heat levels.

As well, the way synthetic species body temperatures are handled is now much more logical. If a species has the synthetic flag, they won't regulate body temperature. Instead, their temperature will constantly go up by a certain amount each second, and be cooled down by the same amount due to the air being colder than them once they reach a certain operating temperature (I'm aiming for roughly 60 degrees C).

This much more naturally implements IPCs overheating in vacuum, as without air their body temperature can't cool. It does mean that a space suit by itself won't keep them cool, as even with a suit, there's no where for the heat to go. I plan on creating a "suit cooling unit" that can be equipped to the suit slot which will cool them down and run off a power cell, most likely.

UPDATE:
I've added some notes for anyone downstream who might want to tweak the infection system.