Improve tests for stores

Current tests for stores rely on a data blob. They should be rewritten to use [factoria models](https://github.com/phanan/factoria) instead.

- [ ] album.js
- [ ] artist.js
- [ ] equalizer.js
- [ ] favorite.js
- [ ] index.js
- [ ] playlist.js
- [x] preference.js
- [ ] queue.js
- [ ] recentlyPlayed.js
- [ ] setting.js
- [ ] shared.js
- [ ] song.js
- [ ] user.js
