PlayerViewController: Improve the previous/next and backward/forward buttons

This merge request brings some improvements to:

• The seek buttons that are now displayed when the media list contains only a single media.
• Pressing these buttons will now display the same information on the screen with the status label as the seek gestures.
• Appending a media to the queue or removing one from it can now impact the display of the player controls.

Screen recordings

Video_Player Audio_Player