user level choices directly in the settings menu.

Also uncouple user level from preferences.  User level is no
longer a preference itself.

* libnautilus-extensions/nautilus-global-preferences.c:
(global_preferences_create_dialog),
(global_preferences_register_for_ui),
(user_level_changed_callback),
(nautilus_global_preferences_shutdown),
(nautilus_global_preferences_startup):
Remove all of the user level ui stuff.

* nautilus-widgets/nautilus-user-level-manager.c:
(user_level_manager_new), (nautilus_user_level_manager_initialize),
(nautilus_user_level_manager_initialize_class),
(user_level_manager_destroy), (gconf_get_user_level_string),
(user_level_set_default_if_needed),
(gconf_user_level_changed_callback),
(nautilus_user_level_manager_get),
(nautilus_user_level_manager_set_user_level),
(nautilus_user_level_manager_get_user_level):
Emit the the "user_level_changed" signal from a gconf callback
instead of "by hand".  Otherwise we are out of whack because of
gconf asyncness.

* src/nautilus-window-menus.c:
(settings_menu_user_level_radio_group_callback),
(settings_menu_user_level_customize_callback),
(settings_menu_customize_callback),
(nautilus_window_initialize_menus),
(user_level_menu_path_to_user_level),
(user_level_user_level_to_menu_path):
* src/nautilus-window.h:
Remove the "General Settings" menu item.  Replace it with a
user level chooser as well as current user level customizer.