[gnome-music] (9 commits) Non-fast-forward update to branch wip/jfelder/grilo-misc-cleanups

[Jean Felder <jfelder src gnome org>]

The branch 'wip/jfelder/grilo-misc-cleanups' 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:

  5456089... grilo: Factor out songs_available logic to TrackerWrapper
  2e2d980... songsview: Remove unnecessary tracker available check
  ceda092... grilo: Define tracker_plugin_available property
  d927d42... grilo: Simplify _on_source_added method
  a303418... grilo: Rename tracker attribute to _tracker_plugin
  cb16b6c... grilo: Use a configuration file

Commits added to the branch:

  c61964a... grilo: Use idle_add for writeback functions (*)
  7bad9df... playertoolbar: Remove clock-tick signal handling (*)
  1d4631a... playlistview: Correct idle_add use (*)
  41a5d3a... grilo: Factor out songs_available logic to TrackerWrapper
  3298a37... songsview: Remove unnecessary tracker available check
  0902cbc... grilo: Define tracker_plugin_available property
  cb957c4... grilo: Simplify _on_source_added method
  277b9f8... grilo: Rename tracker attribute to _tracker_plugin
  ea55536... grilo: Use a configuration file

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