[gtk] (12 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:

  716f626... gtk: Add GtkSelectionModel
  b7e7bf1... gtk: Add GtkSingleSelection
  977c501... testsuite: omit some selection properties
  4099c77... stack: Provide a selection model
  e60cc9f... stack switcher: Use the selection model
  1cb9cb6... a11y tests: Adapt to changes
  0fc5d33... stack sidebar: Use the selection model
  3033e40... stack: Drop the position property
  8ee9f81... selection model: Add a method to query the selection
  3de6998... single selection: Implement query_range

Commits added to the branch:

  31961e2... gtk: Add GtkSelectionModel
  4e98b03... gtk: Add GtkSingleSelection
  93250a2... testsuite: Add selection model tests
  9a47614... testsuite: omit some selection properties
  21b72eb... stack: Provide a selection model
  170d8f0... stack switcher: Use the selection model
  be4be1d... a11y tests: Adapt to changes
  9608fce... stack sidebar: Use the selection model
  b25c6b3... stack: Drop the position property
  e7b57d5... selection model: Add a method to query the selection
  a716cf7... single selection: Implement query_range
  6021eea... Add a test for query_range