Replace some Gtk::UIManager uses with Gtk::Builder and Gio::Menu.

Because GtkUIManager and GtkAction have been deprecated.
menus_and_toolbars: Replace UIManager with Builder.

* examples/book/menus_and_toolbars/examplewindow.[h|cc]:
  Because UIManager (and GtkAction) is deprecated.
  However, we still need to add the toolbar back somehow,
  and the accelerators do not work.
recent_files: Replace UIManager with Builder.

* examples/book/recent_files/examplewindow.[h|cc]:
  Because UIManager (and GtkAction) is deprecated.
  Gtk::RecentAction (GtkRecentAction) is also deprecated but
  without replacement, so we have just removed that from
  the example.
  This is almost an explanation for the GtkRecentAction
  deprecation in GTK+:
  https://mail.gnome.org/archives/gtk-devel-list/2013-September/msg00022.html
  However, we still need to add the toolbar back somehow,
  and the accelerators do not work.
Printing example: Remove use of Stock items.

Stock items are now deprecated in GTK+.
It is annoying, but here is an explanation:
https://mail.gnome.org/archives/gtk-devel-list/2013-July/msg00005.html
Remove the others/stock example.

* examples/Makefile.am:
* examples/others/stock:
  Stock items are now deprecated in GTK+.
  It is annoying, but here is an explanation:
  https://mail.gnome.org/archives/gtk-devel-list/2013-July/msg00005.html
ToolPalette example: Replace Stock Items with Theme Icons.

This is based on the changes in gtk+'s demos/gtk-demo/toolpalette.c