Begin a common WordPress Backbone helpers file.

Moves the `wp.template` helper to `wp-backbone.js`.



git-svn-id: http://core.svn.wordpress.org/trunk@24358 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove unnecessary local variable.


git-svn-id: http://core.svn.wordpress.org/trunk@24359 1a063a9b-81f0-0310-95a4-ce76da25c4cd