[gtk] (13 commits) ...Merge branch 'child-properties-be-gone' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  b14f0b8... grid: Annotate out args as optional (*)
  08d8f2b... print dialog: Stop using gtk_container_child_get (*)
  1f37600... Remove testtitlebar (*)
  f184393... Remove testactionbar (*)
  7f62132... gtk-demo: Stop using child properties (*)
  a97845c... notebook: Stop using child properties (*)
  a26f400... paned: Stop using child properties (*)
  0a4a7b3... testgtk: Stop using child properties (*)
  7cd9ea4... builder-tool: Stop using child properties (*)
  70bf6d4... Drop child property related apis (*)
  ea7a43b... container: Reduce boilerplate (*)
  7699b43... testsuite: Remove packing property tests (*)
  d89df8a... Merge branch 'child-properties-be-gone' into 'master'

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