[gnome-control-center] (17 commits) ...window: Improve transition between panels

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

Summary of changes:

  e225f80... window: Remove unused struct field (*)
  11d721b... window: Cleanup UI file (*)
  7476bef... panel: Add 'folded' property (*)
  48a9141... panel: Add "title" property (*)
  3d06a71... panel: Add empty UI template file (*)
  d2d3669... panel: Add titlebar to panels (*)
  0ab20af... panels: Switch to CcPanel content (*)
  4300a4a... panels: Use new CcPanel helpers for title widgets (*)
  b756f1e... display: Rework titlebar handling entirely (*)
  4073c88... panel: Remove cc_panel_get_title_widget (*)
  5017f3b... shell: Remove cc_shell_embed_widget_in_header (*)
  bcd969f... shell: Remove cc_shell_set_custom_titlebar (*)
  4209c51... window: Remove panel headerbar widgetry (*)
  82c8757... window: Install action to navigate main leaflet (*)
  2c34771... applications: Switch ti AdwWindowTitle (*)
  b11ea45... window: Remove unnecessary calls to gtk_widget_show (*)
  45c7207... window: Improve transition between panels (*)

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