Adding MusicBrainz as a metadata source

[scottfridwin]

Got things roughly working, but still need to work out how the images will be retrieved. Figured I'd open this PR to get some feedback even though it's not ready to merge.

I also added files that make it easier to work in VS Code using a development container to avoid having to install dependencies. Can easily be removed if you'd rather leave them out, but since they don't affect the image at all I left them in for now.