[gtk] (9 commits) ...Merge branch 'wip/exalm/headerbar-title' into 'master'

[Benjamin Otte <otte src gnome org>]

Summary of changes:

  43a453e... headerbar: Remove has-subtitle property (*)
  67822d0... appchooserdialog: Create title and subtitle manually (*)
  fa0509c... filechooserdialog: Create title and subtitle manually (*)
  35d50f8... headerbar: Remove subtitle (*)
  c2e4e1a... headerbar: Remove user-settable title (*)
  739f681... headerbar: Rename custom-title to title-widget (*)
  6b4bed2... builder-tool: Rename GtkHeaderBar:custom-title to title-wid (*)
  ab59562... headerbar: Document GtkBuilder child types, add a title exa (*)
  fa90747... Merge branch 'wip/exalm/headerbar-title' into 'master'

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