[no subject]

- hierarchical docking in paneds and notebooks
- not currently adequate for toolbars/menus
- there is no such central widget -> every item is dockable
- the main container is GdlDock and every dock item is inside a
  GdlDock (even when floating).  As a side effect of this you can dock
  to floating items too
- all items must be bound to a master object (which is automatically
  created/destroyed)
- user dragging is done with pointer grabbing/event monitoring
- outline dragging indication
- layout saving/restoring is provided in a separate object (xml
  format)
- provides widgets to show/hide items, lock/unlock all items at once
  and to save/restore different layouts
- only locked behavior currently implemented
- layout managment is completely separate from the dock objects: all
  necessary information is accessible using gobject property system
  and container methods (even for non-standard dock widgets)
- widget lifetime and hierarchy are handled automatically by the base
  object (GdlDockObject)
- mostly working placeholders