Medical - Add setting to use limb damage for sum of trauma

[LinkIsGrim]

When merged this pull request will:

• Title.
• Cleanup unused vars in handleIncapacitation.

Implementation is a bit lazy:

• Limb DT is not taken into account by the medical menu. For the torso and the head this is an indicator you are over the fatal threshold for sum of trauma, so that should probably be the case for limbs as well.
• Doesn't interact with fracture/limping thresholds at all. Should it?
• Doesn't interact with unconsciousness at all, the setting description is a lie. Unit will just drop dead upon receiving too much damage to the limbs (pain will likely put them under first though, unless it's death by a thousand cuts).

Damage threshold is per-limb because configuring this as a user is a nightmare otherwise. Default is pretty generous to compensate for lack of armor in the limbs of most units.

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[smitt14ua]

Looks like very useful PR for me. Sum of trauma is the most general reason of deaths and we have many complains about it