Rework the relation between videos and songs

[Arthi-chaud]

There is a tight coupling between songs and videos: a song (or a song version) can have 1+ videos, but the videos should have the same name.

This design has some limitations:

• One song cannot have multiple different videos (for example, one song can have 2 completely different videos)
  • E.g. 'Music Gets the Best of Me', 'Take It Off'
• It is frequent for a music video not to use the album/main version of the song, but an edit. This is usually not reflected in the video's title
  • E.g. 'Disrememberance'
• Different edits of the same video can have different names. This will trick the scanner into thinking that there are 2 versions of the song.

We should rework the way we model videos and their relations with songs