o Removed egg_spread_table_dnd_steal_events() api
  o Added apis:
     egg_spread_table_dnd_set/get_drag_enabled()
     egg_spread_table_dnd_set/get_drop_enabled()
    The set/get_drag_enabled() apis use an EggDragEnableMode enumeration
    to decide whether dragging:
      - Is completely OFF
      - Is enabled (dragging starts when and where children dont handle events)
      - Overrides events on top of child widgets
  o Changed signature of 'widget-drop-possible' signal for something more
    useful (added out 'drop_possible' parameter in addition to boolean
    handled return value).
  o Added documentation