Disable ckeditor ACF to fix #705

And to prevent similar issues in the future.

By disabling the html filter ckeditr has integrated, we prevent it from filtering html we want in the editor, like the media gallery classes. In fact, I can't think of a single use case where this filtering might be useful to us.

This did fix #705 (closed) in my dev blog and the editor seemed to still work as expected, but an additional testrun would be nice.