Various bodytemp and frostbite fixes

Fixed a typo where the right foot was called left foot.
Fixed an overlooked change when add_disease functions were changed.
  - Player will no longer get warm body parts instead of frostbite.
  - Feet, hands and mouth are susceptible to cold again.

Added a sanity check to remove hot/cold diseases if the player is not hot/cold.
Fixed frostbite message spam.
Fixed frostbite happening too soon; it now takes 2 hours for frostnip to set in and 4 hours for frostbite to set in instead of 0.2 and 0.4 hours respectively.
Torso and head no longer warm up/cool down faster than other body parts (expected torso/head to stay warmer, when in fact they got colder fast as well).
Lying down now uses floor tiles for warmth in the same way sleeping does (suggested in #8351).
There is a terrain flag "SWIMMABLE" that is used for swimming. It's currently set for t_water_sh, t_water_dp, t_swater_sh, t_swater_dp, t_water_pool and t_sewage. Could this be used as a simpler and generalized way to check this? Otherwise you should include t_swater_sh and t_swater_dp (salt water).