[gtk] (7 commits) ...Merge branch 'wip/exalm/window-headerbar' into 'master'

[Benjamin Otte <otte src gnome org>]

Summary of changes:

  2240eb5... header-bar: Stop showing application menu (*)
  cead405... header-bar: Don't assume there's only one icon (*)
  016eac0... header-bar: Track window icon changes (*)
  451c327... window: Introduce actions for window buttons (*)
  610d579... headerbar: Update window buttons automatically (*)
  7c4694c... window: Stop listening to headerbar title changes (*)
  389575e... Merge branch 'wip/exalm/window-headerbar' into 'master'

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