Improved food groups and made them defined by json files
 * Food groups are defined by json files in /config/SpiceOfLife/
 * Added support for using food groups as blacklists/whitelists (closes #7)
  * If config option 'use.food.groups.as.whitelists' is true, items not in a food group will be excluded from diminishing returns
  * If a good group has 'blacklist' set to true, items in it will be excluded from diminishing returns
 * Added support for different diminishing returns formulas per food group (closes #8)