use schema.title as placeholder for additionalProperties if schema_arr have one choice

jsonform/gadget_json_generated_form_child.js

@@ -1158,6 +1158,11 @@
       .push(function (schema_arr) {
         var queue = RSVP.Queue(),
           property_name;
+        if (checkSchemaArrOneChoise(schema_arr) && schema_arr[0].schema.title) {
+          title = schema_arr[0].schema.title;
+          // XXX change placeholder again
+          input.placeholder = "name of " + title;
+        }
         for (property_name in json_document) {
           if (json_document.hasOwnProperty(property_name) && !used.hasOwnProperty(property_name)) {
             used[property_name] = "";