[gtk] (19 commits) ...Merge branch 'matthiasc/for-master' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  6153efd... Document GTK_ACCESSIBLE_ROLE_NONE (*)
  3151906... docs: Small corrections to the a11y overview (*)
  d7794bf... docs: Add some more to the migration guide (*)
  48bb920... a11y: Treat PRESENTATION like NONE (*)
  8f10026... scale: Hide internal structure from a11y (*)
  ca9b068... switch: Hide internal structure from a11y (*)
  14a64c7... levelbar: Hide internal structure from a11y (*)
  d3089eb... progressbar: Hide internal structure from a11y (*)
  b9ae54c... separator: Remove unnecessary code (*)
  087c007... menubutton: initial accessibility setup (*)
  2bfd419... popovermenu: Initial accessibility setup (*)
  758bcd5... popovermenubar: Initial accessibility setup (*)
  f96a1cf... modelbutton: Initial accessibility setup (*)
  3e43dda... modelbutton: Recreate our AT context (*)
  88eb3a9... atspi: Give model buttons a click action too (*)
  5f8c6d2... a11y: Document roles used in menu (*)
  bcbc615... a11y: Document abstract roles (*)
  800eb76... linkbutton: Use the LINK role (*)
  daf3b3a... Merge branch 'matthiasc/for-master' into 'master'

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