Mark a track as favorite or skip

Alrighty, so after some discussion on Slack here's some thoughts:

We do want some way to rate a song as 👎 or ⏩ because of the case where you have like a skit or an intro in an album and you don't want to delete the song, but you also don't want it play in shuffle.

There's some thoughts around the usefulness of 👍 / ❤️ because we might be able to know which songs are your favorites more accurately than you do based on things like play count or how often you add them to a playlist. But it does sound like some people want the ability to mark their favorites explicitly.

So it sounds like the current stance is that 5 stars plus unrated is overkill and it's unclear what it means. But we do want to have 3 states: positive, neutral, and negative.

There's some discussion about using ⏩ instead of 👎 because it seems more explicit about the implication of what the rating means: We're going to skip these songs in shuffle. But on the other hand 👎 is more of a flexible metaphor when you're making smart playlists, but it will require some extra explanation to make sure it's clear what it implies.

The issue names no files, tests, or entry points. First resolve whether the states mean favorite, rating, or shuffle skipping, and define the expected behavior for smart playlists and shuffle playback. Done should include an agreed interaction and behavior that can be implemented and tested.

Written by the indexing model from the issue text.