Use add_node() instead of add_menu() in core

[linuxologos]

It's clear through class-wp-admin-bar.php and Nacin ​has stated this too:

The API previously emphasized add_menu(), but this can be confusing, so add_node() is now being promoted a bit more.

Another step towards this would be that the core used add_node() instead of add_menu() when building menu items in admin-bar.php.

Proposed patch replaces all references to the add_menu() method with the add_node() one. (Also some code structure modifications for wp_admin_bar_appearance_menu().)

Ryan, you game?