Add Enumerator source to import

In Play 2.3.1, I have to add `import play.api.libs.iteratee.Enumerator` to run the controller.
Meaning there is that 'Simple results' (topic of the section) are defined by class `play.api.mvc.Result`. If your suggestion is that required imports would be nice, it would be better in code sample (file 'code/ScalaActions.scala').