https://ckeditor.com/docs/ckeditor4/latest/guide/dev_toolbar.html
https://ckeditor.com/docs/ckeditor4/latest/guide/dev_toolbarconcepts.html
https://sdk.ckeditor.com/samples/fileupload.html#
https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_config.html#cfg-filebrowserImageUploadUrl