Add ItemArray conversion for the string name.

Since numerical item ids are deprecated, we should allow users to start using the name of the item as supported by the server implementation they are using. This commit allows ObjectGenerator to interpret a new field "id", containing the string ID of the item, and if it is present the old integer "type" will be ignored. ObjectGenerator will also write the "id" to any new item arrays it creates, but will continue to fill in "type" for compatibility.