[gtk] (18 commits) ...Merge branch 'ebassi/for-master' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  428ec29... a11y: Unrealize ATContext on dispose() (*)
  3b2cd97... a11y: Implement missing atspi.Component getters (*)
  65d29e0... a11y: Realize parent ATContext for the stack page (*)
  95ee5ff... a11y: Add more ARIA/AT-SPI role translations (*)
  033791b... a11y: Translate ARIA windows to AT-SPI frames (*)
  04c4d29... a11y: Skip unlabelled structural roles (*)
  27b9b2e... a11y: Use the window title as its label (*)
  40c0826... a11y: Mark more containers as structural elements (*)
  73b14a3... a11y: Do not leak the ATContext in GtkStackPage (*)
  877a7f9... a11y: Protect should_present() from empty contexts (*)
  526f1e3... a11y: Use GROUP role for GtkNotebook (*)
  2285382... a11y: Create AtSpiRoot on realization (*)
  292576f... a11y: Defer to the GtkAccessible's implementation (*)
  9052f6d... a11y: Rework ownership and lifetime of GtkATContext (*)
  8157717... a11y: Add missing fallback for accessible-role getter (*)
  9ac4a7d... a11y: Simplify GtkModelButton (*)
  08d59d3... docs: Add "Accessibility" section to various widgets (*)
  5d9799d... Merge branch 'ebassi/for-master' into 'master'

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