Add customisation for artwork and player name

[Scepticalist]

Trying to customise the player and there's a couple of features that might be useful:

• Expand option for player name to include all the players in the group (use a hyphen separator?), not just the number of players
• Could there be a switch to enable the expanded player (cover) even if there's no artwork present and a way to supply that image? I'd like all players to be similar when playing, regardless of the source. e.g. like in the image below, which isnt possible with mmp - with a TV source (Living Room) the player would be compressed with no cover art available.