dbus-manager: add a skeleton of NautilusDBusManager
dbus-manager: implement the CopyURIs method
dbus-manager: add an EmptyTrash operation
fixed: Adjust Default _zoom level always get the last "old" value

The callback function update_auto_enum should be connected before the default_zoom_level_changed, otherwise the new_level always get the last "old" value in default_zoom_level_changed and the desktop-view display strange.