Fix formatting nits
Zotero.Utilities.Internal.defineProperty => Zotero.defineProperty
Restore Zotero.Item.parentItemID and Zotero.Item.parentItemKey
getClassForObjectType => getObjectsClassForObjectType
Add Zotero.DataObject.ObjectsClass property
Throw if calling Zotero.DataObject.prototype._saveData/_finalizeSave
These must be overridden in derivative classes
Fix ObjectsClass syntax error
Fix leftover Zotero.Utilities.Internal.defineProperty