CKEditor 4.1 OEmbed fix

Fixed the "Uncaught TypeError: Cannot read property 'isBlock' of undefined" error thrown by the plugin in the CKEditor 4.1.

Also changes the config.oembed_WrapperClass to config.oembed_Wrapper, and from now you can also specify any custom tag, style and/or class for the wrapping element like:
config.oembed_Wrapper = '<p style="text-align:center">';