[gnome-music] (18 commits) ...grltrackerwrapper: Consolidate art queries

[Marinus Schraal <mschraal src gnome org>]

Summary of changes:

  5bc9a5e... coreartist: Rework retrieval (*)
  225995b... artistart: Split out retrieval and cache storage (*)
  0c11667... artcache: Unify DefaultIcon and _make_icon_frame (*)
  87b962b... artistartstack: Disconnect cache callback (*)
  dc0a5ac... artistartstack: Remove DefaultIcon use (*)
  25cd007... artistartstack: Remove unused variable (*)
  c490e5f... artstack: Renamed from ArtistArtStack (*)
  51d59ba... artstack: Add default size setter (*)
  f22f41a... corealbum: Add thumbnail property (*)
  9992267... Rename StoreArtist to StoreArt (*)
  1e00203... Restore embedded art support (*)
  0d3bfad... artstack: Disconnect notification on coreobject change (*)
  0d17ea0... coresong: Add thumbnail property (*)
  73c5190... mpris: Use CoreSong thumbnail property (*)
  9c4a66d... utils: Add ArtSize enum (*)
  eb8cafc... Remove coverstack.py and albumartcache.py (*)
  765bebf... grltrackerwrapper: Clarify function name (*)
  2bff0d6... grltrackerwrapper: Consolidate art queries (*)

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