[gtk] (12 commits) ...Merge branch 'dropdown-for-merge' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  371dab5... Add GtkDropDown (*)
  d3aad3b... filechooser: Use a dropdown for the filter combo (*)
  496e673... filechooser: Use a dropdown for choices (*)
  99c98d0... inspector: Use dropdowns in property editor (*)
  6346fa9... inspector: Use a dropdown for attribute mapping (*)
  3054120... inspector: Use a dropdown for controllers (*)
  54cdafd... inspector: Use a dropdown for size groups (*)
  b331e29... inspector: Use dropdowns in the visual page (*)
  336b30c... gtk-demo: Add a large grid demo (*)
  9c849d2... docs: Update the list widget overview (*)
  fc9462d... Add some tests for new GtkBuilder syntax (*)
  d833f4a... Merge branch 'dropdown-for-merge' into 'master'

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