Disc could be detailed objects

[Arthi-chaud]

Currently, discs are virtual objects, as they are only referred to by track's disc's index

From a die-hard collector point of view, in a box-set, the discs within can be differentiated using a name, an illustration etc.

Therefore, a Disc model should be developed. It would store tracks, have an optional name & illustration, a index in the parent release. This would be a little overkill in 95+% of releases