* Updated `PlayerQueueInfo` model to remove repeated items when retrieving player queue information. For some reason, the Spotify Web API will return up to 10 duplicate items with the same information. For example: if there is only 1 item in the queue, then 10 duplicate items are returned by the Spotify Web API; if there are 5 items in the queue, then 5 duplicate items are returned by the Spotify Web API. We will check for this scenario, and only return non-duplicate items if so.
* Updated `PageObject` model to include the `DateLastRefreshed` property, which contains the date and time items were was last refreshed in unix epoch format (e.g. 1669123919.331225). A value of zero indicates the date was unknown. Note that this attribute does not exist in the Spotify Web API; it was added here for convenience.
* Added `SpotifyClient.AddPlayerQueueItems` method that will add one or more items to the end of the user's current playback queue.
* Marked `SpotifyClient.AddPlayerQueueItem` method as deprecated; use the new `AddPlayerQueueItems` method instead.