MBS-5658: Don't set track artists to Various Artists

When the release editor is seeded, users can specify a TOC which
means blank tracks will be created. By default, these blank tracks
share the same artist as the release artist. However, if they user
chooses 'Various Artists' as the release artist, then all the
tracks should have a blank artist credit, as this release should
have different artists per track.
Merge branch 'beta' into mbs-5658

Conflicts:
	lib/MusicBrainz/Server/Wizard/ReleaseEditor/Add.pm