Fix 'Play next in queue' and 'append to queue' not working in shuffle mode

The addition of the shuffledList alongside the mediaList wasn't complete in !1255 (merged) so many areas in the code still only reference mediaList when they should be referencing shuffledList if shuffle mode is on. This MR only addresses this enough to close issue #1852 (closed).

The behavior after this change is as follows: 'Append to queue` and 'Play next in queue' now affect both the shuffled list and non shuffled list. So if shuffle mode is on and you long press on a media > 'Play next in queue', that media will still be next in queue if shuffle mode is turned off.

If the media is already in the shuffled queue at some index, the media is appended to the queue or added next in queue as a duplicate. This matches the current behavior for the non-shuffled queue.

Closes #1852 (closed)