implement spotify embeds

[A-Schmid]

Actually quite easy if we have the spotify IDs of the songs.
However, even the small player starts to look like shit when under 80px high.
Either we keep it this size, or we use a workaround solution (yay).
Idea:

• place spotify embeds in hidden div
• use the spotify iframe API (https://developer.spotify.com/documentation/embeds/guides/using-the-iframe-api/) together with a custom button to control the hidden widget
• no idea if this works