1. Look up now follows your mob (no more auto-removal when you move,
only when you go below a solid tile). Maybe add a hotkey?
2. Made the codebase work with the latest version of spacemandmm lint.
3. Advanced kits don't work on robotic limbs.
4. Density shifting should now always use set_density. Ported
TRAIT_UNDENSE from CM to better control the density of living mobs.
Fixes weird shifting behaviour with wall leaning -- what was happening
is that mob density was getting reset to TRUE because the mob wasn't
lying down.
5. TGUI say light prefs actually save.
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Co-authored-by: Matt Atlas <liermattia@gmail.com>
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