[gtk] (11 commits) ...Merge branch 'overlay-cleanup' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  b70cd64... gtk-demo: Move the blur demo code here (*)
  d291dff... gtk-demo: Fix the decorative overlay example (*)
  1818f55... overlay: Drop the blur support (*)
  f57e66c... overlay: Drop the index child property (*)
  3487ebe... remove tests that no longer work (*)
  2e5ccce... Make gtk_widget_set/get_can_pick public (*)
  f8609ef... testoverlay: Use gtk_widget_set_can_pick (*)
  f202707... gtk-demo: Use gtk_widget_set_can_pick (*)
  beb8d36... overlay: Remove gtk_overlay_set_overlay_pass_through (*)
  4e97417... Update migration guide for pass-through (*)
  41c0ac1... Merge branch 'overlay-cleanup' into 'master'

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