Improve playlist template

[vojtaholik]

cover for 3 scenarios:

• has an artwork (https://twitter.com/eggheadio/status/1318696503347654657?s=20) (template similar to course card)
• doesn’t have an artwork and is “nested playlist”
• doesn’t have an artwork

When playlist uses a tag image the url will look like : https://d2eip9sf3oo6c2.cloudfront.net/tags and when it has art it's https://d2eip9sf3oo6c2.cloudfront.net/playlists/square_covers. Could make a helper like hasDefaultImage that peeked the URL for `/tags