Use Croogo.bootstrapComplete event to start editor setup

Since `Wysiwyg.actions` has been setup by every plugin bootstrap.php,
attaching helpers now does not depend on plugin load order.

Closes #409
Add forgotten file Event/WysiwygEventHandler.php *facepalm*
Fix: Add span10 class
Since cakephp/cakephp@5d4bb9c2, we can use the result of dispatch()