[RossBrunton]

Did a few checks for this and it seems to Just Work.

Specifically:

• Using the scroll wheel on the widget adjusts the volume as expected.
• The icon updates based on volume/mute state.
• Each instance can be opened, and shows its own media controls (which each see every media).
• Each instance sees and generates its own settings file.

The only thing I've not been able to test is the new(?) JS mpris player interface since I'm on an older Cinnamon version, but it doesn't look like there'll be any issues from giving the code a cursory look over.