Improve handling of album art for downloaded tracks

[el-tiuri]

It’d be great if the album art for downloaded tracks would be downloaded and used everywhere (album grid, fullscreen player), rather than fetching the album art again. The artwork does show up in the miniplayer though, so perhaps a full quality version does already get cached but is just not used in some views.

See attached screenshot

[leinelissen]

Hey @el-tiuri, thanks for reporting this. This is a weird one, as they use the same image, precisely because we want to cache a single version. I've received other reports around artwork for offline tracks, so when I find the issue, I'll link these two up.