Initial supported for scripted ingredients, not fully tested.

This adds a few additional interface functions, to be defined in:
scripts/global/cooking.lua, or
_mods/XYZ/scripts/cooking.lua

Added functions:
cookFailure(a,b,c) - Called when no recipe could be found for ingredients a,b,c
getIngredientString() - Called by the menu. Expected to return effects description
                        for scripted ingredient..
useIngredient(name) - Called when a scripted ingredient will be eaten.
                      Return true to eat.

Use a line like this in ingredients.txt:
LuaLoaf sealoaf Loaf (script)
to enable calling useIngredient() upon eating.