[gtk] (9 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:

  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
  0a77f54... stack switcher: Allow alternative models
  16f889c... Add a silly example

Commits added to the branch:

  32eb891... gtk: Add GtkSelectionModel
  5b2de24... gtk: Add GtkSingleSelection
  24feaa6... testsuite: Add selection model tests
  7ab30c9... testsuite: omit some selection properties
  2ce7ee9... stack: Provide a selection model
  7880fda... stack switcher: Use the selection model
  60138cd... a11y tests: Adapt to changes
  339041c... stack sidebar: Use the selection model
  fe83a25... stack: Drop the position property