update all *.ui files
panel-image-menu-item: remove use of GtkSettings:gtk-menu-images

This is deprecated so remove use of this property and use default
value - FALSE.

PanelImageMenuItem was added only for main-menu and menu-bar
applets. In future these applets might get preferences dialogs. If
it will happen then most likely this will be configurable option.
remove bonobo info from docs