Complete refactoring to move Recipes into Items

* Changed "version" to "dataVersion" in data format
* Changed the "modName" and "modVersion" fields on the ModVersion
  class to remove the "mod" prefix and changed the data format to
  match
* Change the Stack class to use the itemSlug instead of the item
  itself
* Update the ModVersion and ModPack classes to include methods for
  recording a correspondence between slugs and names. Update code
  which displays items from stacks to use these methods to determine
  display names.
* Add a reference from Recipe back to the item it creates

test/inventory_parser.test.coffee

@@ -37,6 +37,6 @@ describe 'InventoryParser', ->
 
     it 're-uses the given inventory object', ->
         inventory = new Inventory
-        inventory.add new Item(name:'String'), 8
+        inventory.add 'string', 8
         result = parser.parse '4 Wool', inventory
         result.toList().should.eql [[8, 'string'], [4, 'wool']]