Allow ckeditor config override via contenttype HTML

Settings are added as json to the data-ckconfig attribute of the textarea 
and are used as override inside bolt.js. see also #1233 

```
// Example under "Showcases" contenttype
        html:
            type: html
            height: 333px
            ckconfig:
                height: 300
                # contentsCss: ["directory/aa", "/directory/bb"]
                autoGrow_minHeight: 300
                autoGrow_maxHeight: 900
```