Better configuration

Recipe for cotton added.
Mushroom_light added.
Spreading for Asparagus changed.
Support for Petz added.
Function group_add available to better support foreign nodes.
Replaced function minetest.override_item with cucina_vegana.add_group for better compatibility.
Settings now configurable about Main-Menu or minetest.conf.
Rice grows on default:dirt_with_grass too.