Cold drinks!

This PR gives minifriges the ability to chill certain foods (primarily
beverages) and give them the (cold) flag which improves their morale
boost by 50% - or gives them a small morale boost if they have a
negative morale value.
The cold flag wears off with time (about an hour out of the fridge) and
is tied to a new comestible flag ("EATEN_COLD") with all the relevant
morale calculations taken care of in player.cpp.