[gtk] (13 commits) Non-fast-forward update to branch stack-fixes

[Matthias Clasen <matthiasc src gnome org>]

The branch 'stack-fixes' 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:

  00581c6... Keep GtkSingleSelection private for now
  ea403ab... Fix GtkSingleSelection property notification
  694bb89... stack: Provide a selection model
  1b7d2a9... stackswitcher: Use a model
  b4d600e... sidebar: Use a model
  f18027f... stack: Drop the position property
  4df0853... Fix problems with the no-selection state

Commits added to the branch:

  7621914... Fix GtkSingleSelection property notification
  de11271... stack: Provide a selection model
  35bba74... stackswitcher: Use a model
  e11373e... sidebar: Use a model
  d0bd43e... stack: Drop the position property
  9deb7f1... Fix problems with the no-selection state
  3529dee... single selection: Add a selected-item property
  84f243a... Add the selection models to the docs
  de070d3... fixup
  0857a8a... selection model: Add a doc comment
  b715d59... stack: Use gtk_single_selection_get_selected_item
  a0c7ac8... stack sidebar: Use gtk_single_selection_get_selected_item
  d84829a... stack switcher: Use gtk_single_selection_get_selected_item