[grilo-plugins] (5 commits) Non-fast-forward update to branch wip/jfelder/theaudiodb-artist-art

[Victor Toso <victortoso src gnome org>]

The branch 'wip/jfelder/theaudiodb-artist-art' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  3d8839b... theaudiodb: Add a unit test
  d222b2d... theaudiodb: Use the correct variable for album
  cd364fc... theaudiobd: Add support for artist art

Commits added to the branch:

  af7d6b6... tracker: Remove musicbrainz keys from the list of writable  (*)
  7c29d5e... tracker: Use tracker:ExternalReference to retrieve musicbra (*)
  1025509... theaudiodb: Add a unit test
  6d15686... theaudiodb: Use the correct variable for album
  1d6c590... theaudiobd: Add support for artist art

(*) This commit already existed in another branch; no separate mail sent