ResourceGroups and TrackReleases

Track Releases need to be communicated in each NewReleaseMessage.

In ERN-3 all Releases – whether album Releases or whether Track Releases – are described in the same way. And this means that while a TrackRelease can only contain one primary Resource, it still needs to contain a ResourceGroup.

In ERN-4, however, main/album Releases are described in the Release composite while Track Releases are described in the – very much simplified – TrackRelease composite, which does not have the ability to provide resource group information