Ckeditor is not correctly binded to newly added slide item #30

Describe the bug
When adding a new slide item in a slider with the button "Add another Slide", the content field is not a ckeditor field but instead a basic textarea.

To Reproduce
Steps to reproduce the behavior:

1. Go to any cms page
2. Add or edit a Slider to the page
3. Add a new slide item
4. The content field is a basic textarea
5. Save the slider with the new slide
6. Go back to edit the plugin, the previously added new slide has a Ckeditor widget on field 'content' as expected

Expected behavior
The slide item field 'content' should always be a Ckeditor widget.

Versions:

• Python: Any
• Django: Any
• DjangoCMS: Any

Additional context
There is some Javascript error when adding new field, i don't know yet why it does not work as expect since this is automatically done from Django inline form system.