[Feature request] Filter by number of times a track appears

[dbaranger]

Just in case anyone decides to resurrect this excellent project and add more features!

It can happen that a track appears in multiple sources. Usually we want to remove the duplicates with 'de-dup'. Sometimes, though, I actually want to know what those duplicate tracks are, or say maybe I want to order tracks by the number of times they appear. This isn't API information, just information already present in the data. It would be great to be able to see this and filter/sort based on it!