Updates to make DYE work with Django-CMS 3.

Note that:

* some CMS plugins have changed names, so we need some conditional code in
  cookiecutter if we want to support Django-CMS 2 going forward.
* not all plugins tested yet.
* cms_redirects may be superceded by built-in functionality now.
* going back to official releases of ckeditor may undo bug fixes in our fork.