added equipped and owner to item sheet

Additions:
- added equipped checkbox to item sheet
- added item owner to item properties list
- added some translations
- added some TODOs

Changes:
- item properties owner, equipped, quantity, storageLocation
  are only shown if item is owned by an actor
- moved item properties price and availability
  to details tab
- shortened ItemEquipped translation
- added item.actor and item.isOwned property values
  to data returned from DS4ItemSheet.getData
  (properties aren't accessible in Handlebars)

src/lang/en.json

@@ -16,7 +16,8 @@
     "DS4.Quantity": "Quantity",
     "DS4.PriceGold": "Price (Gold)",
     "DS4.StorageLocation": "Stored at",
-    "DS4.ItemEquipped": "Item equipped?",
+    "DS4.ItemEquipped": "Equipped?",
+    "DS4.ItemOwner": "Owner",
     "DS4.ItemAvailability": "Availability",
     "DS4.ItemAvailabilityHamlet": "Hamlet",
     "DS4.ItemAvailabilityVilage": "Village",