Add Backbone property to the wp-backbone namespace. See #24424.


git-svn-id: http://core.svn.wordpress.org/trunk@24367 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Branch the generic JS utilities from the Backbone commands. See #24424.


git-svn-id: http://core.svn.wordpress.org/trunk@24368 1a063a9b-81f0-0310-95a4-ce76da25c4cd