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/templates/actor/partials/items.hbs

@@ -1,4 +1,6 @@
-{{!-- TODO: Where possible use icons with complete names as hovers instead of long names --}}
+{{!-- TODO: For items list: only show header, if list is not empty --}}
+{{!-- TODO: Reduce code duplications --}}
+{{!-- TODO: Change from flex layout to grid layout --}}
 {{!-- Tab with overview and quick-actions on owned items --}}
 <div class="tab items" data-group="primary" data-tab="items">