Gdk::Device: Add get_last_event_window().
Application: Add get/set_accels_for_action() and list_action_descriptions().
StyleContext: Add get/set_scale().
Window: Ignore some private or obscure functions.
Application: Add set_accel_for_action().

* gtk/src/application.[hg|ccg]: So we don't need to create
  a vector for just one accel.