Like MBS-12170 but for the release label(s).

Many MusicBrainz Releases are being entered with 190-210 release countries, and many users find this data worthless. Given this direction the data is going in, some users are going to find it more useful to store the country of the label(s), which is currently constrained to a single country per label. However, this data is not currently included in the webservice results for a release lookup. I think it should be, rather than force clients to make an additional webservice call per release label that appears on the release.