json_form: XXX use encoded json as string, not a javascript object

( this might also be causing problems, but it's what I used in the POC )

bt5/erp5_json_form/SkinTemplateItem/portal_skins/erp5_json_form/jsonform.gadget.js.js

@@ -790,7 +790,9 @@
         editable: options.editable === undefined ? true : options.editable
       };
       if (options.value !== undefined) {
-        z.value = JSON.stringify(options.value);
+        // XXX shouldn't it already be encoded ???
+        // z.value = JSON.stringify(options.value);
+        z.value = options.value;
       }
       return this.changeState(z);
     })