Menu polishing

Now that the mechanics part of this works, I can focus on cleaning up
the menu part of it.  Ditched the last of the huge string of yes-no
queries from the old version, now examining the kitchen unit gives us a
nice, neat menu instead.  Also renamed the got_water bool in this
function to used_feature to avoid any confusion, and altered it's
placement in the code order to prevent the examine vehicle menu from
popping up after using the kitchen unit functions.  Now all that's left
is to add in the welding rig code, and finally vehicle-mounted equipment
will be just as useful as carried equipment!