[Desktop] Add an append to play queue button

We should have a button to append a track to the play queue as it would save time and make it easier to quickly add more tracks to the queue. Perhaps we can bring back the '+' icon since we have a new icon for saving tracks and it is a good symbol to represent the action.


This feature would help me so much! I hate having to right click for the context menu every time I want to add a song to the queue. It's even worse on mobile.