Updated get_queue code to work with data structure changes in upstream

This simple change changes the get_queue method so that it works with the (data structure changes in upstream soco)[https://github.com/SoCo/SoCo/pull/93]. In upstream get_queue now returns a list of QueueItem as supposed to earlier where it was a list of dicts. In these QueueItems the title, album and creator info is now available as named attributes.