[gnome-music] (16 commits) ...headerbar: Add selection-mode-allowed prop

[Marinus Schraal <mschraal src gnome org>]

Summary of changes:

  85066a1... artistalbumswidget: Make artist variable private (*)
  9cf6674... artistalbumswidget: Fix variable rename fallout (*)
  fd255fe... artistalbumswidget: Make selection-mode a property (*)
  0d38c63... artistalbumwidget: Add select_{all,none} (*)
  6af5634... artistalbumwidget: Mark create_disc_box private (*)
  f913a0a... selectiontoolbar: Add items-selected property (*)
  adbc3ab... selectiontoolbar: Add add-to-playlist signal (*)
  d6e82de... artistalbumswidget: Remove unused argument (*)
  dc34129... disclistboxwidget: DiscBox minor cleanups (*)
  0924388... baseview: Set selection-mode prop on state request (*)
  6456eee... headerbar: Bind selection-mode prop directly to button (*)
  5c1c512... baseview: Connect to class selection-mode property (*)
  e5ad6cc... headerbar: Handle cancel button in class (*)
  8903fbc... albumwidget: Add selection-mode property (*)
  8dbbfcb... disclistboxwidget: Remove selection-toggle signal (*)
  7c9674f... headerbar: Add selection-mode-allowed prop (*)

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