[gtk] (8 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:

  c106436... gtk: Add GtkSelectionModel
  d4f4626... gtk: Add GtkSingleSelection
  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
  4965428... stack switcher: Redo the radio logic
  6e640ae... stack switcher: Remove a redundant style class
  cb58d08... stack switcher: Be robust in destruction
  da9b462... stack sidebar: Only use selection model api

Commits added to the branch:

  716f626... gtk: Add GtkSelectionModel
  271354e... gtk: Add GtkSingleSelection
  b395589... stack: Provide a selection model
  eb0b1c5... stack switcher: Use the selection model
  a561a6c... stack sidebar: Use the selection model
  196b371... stack: Drop the position property
  e4b226c... stack switcher: Remove short-circuiting
  de92a16... stack sidebar: Remove short-circuiting