Plot negativity of listening habits

[cheshire137]

Like the 'Positive' line, the inverse of the valence metric could maybe be used to show a rise in negativity:

A measure from 0.0 to 1.0 describing the musical positiveness conveyed by a track. Tracks with high valence sound more positive (e.g. happy, cheerful, euphoric), while tracks with low valence sound more negative (e.g. sad, depressed, angry).

-- https://developer.spotify.com/web-api/get-several-audio-features/

Idea from @pifafu! ❤️